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Evaluation of mechanisms for the formation of cyclopropanes from pyrazolines and the interconversion… McKinley, James William 1972

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EVALUATION OF MECHANISMS FOR THE FORMATION OF CYCLOPROPANES FROM PYRAZOLINES AND THE INTERCONVERSION OF CYCLOPROPYL KETONES AND DIHYDROFURANS BY JAMES W. McKINLEY B. S c , U n i v e r s i t y of B r i t i s h Columbia, 1967 M.Sc, U n i v e r s i t y of B r i t i s h Columbia, 1969 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY i n the Department of CHEMISTRY We accept t h i s thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA A p r i l , 1972 In p r e s e n t i n g t h i s t h e s i s in p a r t i a l f u l f i l m e n t o f the requirements f o r an advanced degree at the U n i v e r s i t y of B r i t i s h Columbia, I agree that the L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e f o r re ference and s tudy . I f u r t h e r agree t h a t p e r m i s s i o n fo r e x t e n s i v e copying o f t h i s t h e s i s f o r s c h o l a r l y purposes may be granted by the Head of my Department or by h i s r e p r e s e n t a t i v e s . I t i s understood that copying o r p u b l i c a t i o n o f t h i s t h e s i s f o r f i n a n c i a l ga in s h a l l not be a l lowed wi thout my w r i t t e n p e r m i s s i o n . Depa rtment The U n i v e r s i t y o f B r i t i s h Columbia Vancouver 8, Canada Date ABSTRACT A s e r i e s of 3-methyl-3-acetyl-l-pyrazolines were prepared and t h e i r product d i s t r i b u t i o n s were determined. Part of t h i s s e r i e s included t e t r a s u b s t i t u t e d 1-pyrazolines uniquely substituted at a l l three r i n g carbons. These pyrazolines have the advantage i n that they can decompose to four isomeric cyclopropanes, and thus information about the degree of re t e n t i o n or i n v e r s i o n at both C-3 and C-5 of the s t a r t i n g pyrazoline was obtained. The product d i s t r i b u t i o n s from the d i r e c t and s e n s i t i z e d photolysis of these pyrazolines were explained by invoking d i r a d i c a l s which r e t a i n the i n t e g r i t y of the pyrazoline precursor. The formation of dihydrofurans from cyclopropyl ketones was approached by using cyclopropanes uniquely substituted at a l l three r i n g carbons and thus information was derived about the stereochemical pathway f o r t h i s conversion. The rea c t i o n was inve s t i g a t e d both thermally and photochemically and therefore complementary r e s u l t s were obtained f o r the two modes of r e a c t i o n . A step-wise mechanism f o r the r e a c t i o n was favoured i n which d i r a d i c a l s that r e t a i n the i n t e g r i t y of the cyclopropane precursor were used to explain the product d i s t r i b u t i o n s . In a d d i t i o n , the conversion of a cyclopropyl ketone to a dihydro-furan was inve s t i g a t e d by a k i n e t i c study and was found to proceed with a high a c t i v a t i o n energy of 48.1 Kcal/mole (log A = 14.9). These a c t i v a t i o n parameters are consistent with a step-wise mechanism i n v o l v i n g d i r a d i c a l s that r e t a i n the i n t e g r i t y of the cyclopropane precursor. - i i i -TABLE OF CONTENTS Page I. INTRODUCTION 1 1. Cyclopropanes from 1-Pyrazolines 2 (a) The Beginning of a Problem 2 (b) A d d i t i o n a l Pyrazoline Decompositions 9 (c) B i c y c l i c Pyrazolines 17 (d) T r i p l e t S e n s i t i z a t i o n 21 2. Cis-Trans Isomerization of Cyclopropanes 23 3. Cyclopropyl Ketone and Dlhydrofuran Interconversion 29 4. Purpose of Present Research 31 I I . RESULTS 32 1. Preparation and I d e n t i f i c a t i o n of Pyrazolines 32 2. D i s t r i b u t i o n and I d e n t i f i c a t i o n of Products 48 (a) Method of Decomposition 48 (b) P h o t o l y t i c Control Experiments 48 (c) Decomposition of 3,4-Dimethyl Pyrazolines 98 and 99 49 (d) Photolysis of 3,5-Dimethyl Pyrazolines 19_ and 20 5 2 (e) P h o t o l y s i s of Tetrasubstituted 1-Pyrazolines . 54 3. Stereochemical Assignment to the Cyclopropyl Ketones 57 4. Rearrangement of Tetrasubstituted Cyclopropanes.... 61 (a) General 6 1 (b) Thermal and Photochemical Results 64 (c) Control Runs 72 - i v -Page 5. K i n e t i c Studies . 73 (a) General 73 (b) Experimental Conditions 75 (c) C a l c u l a t i o n of Results 78 (d) Attempted c i s - t r a n s Studies of Cyclopropyl Ketones 132 and 133 78 I I I . MECHANISTIC DISCUSSION 80 1. Pyrazoline Decomposition 80 (a) General 8 0 (b) C i s - and Trans-3,4- and 3,5-Pyrazolines 82 (i ) Non-Cyclopropane Forming Reactions 82 ( i i ) Cyclopropane Forming Reaction 85 (c) Tetrasubstituted 1-Pyrazolines 90 (i ) Non-Cyclopropane Forming Reactions 90 ( i i ) Cyclopropane Forming Reaction 92 2. Rearrangement of Tetrasubstituted Cyclopropyl Ketones 96 (a) General 96 (b) Consideration of Concerted Process 98 (c) Consideration of Step-wise Process 101 (d) K i n e t i c s 109 IV. EXPERIMENTAL 117 1. General 117 2. Preparation of S t a r t i n g Materials 118 (a) 3-Methyl-3-pentene-2-one, (Z)-(100) 118 - v -Page (b) 3-Methyl-4-phenyl-3-butene-2-one, (E)-(102)... 118 (c) Benzaldehyde hydrazone 118 (d) N-nitroso-N-methyl-urea 118 (e) N-nitroso-N-ethyl-urea 118 (f) Diazomethane and Diazoethane 119 (g) Phenyl diazomethane 119 3. Cis-3,4-dimethyl-3-acetyl-l-pyrazoline (98) 119 (a) Preparation and I d e n t i f i c a t i o n 119 (b) P y r o l y s i s and Product I d e n t i f i c a t i o n 120 (c) D i r e c t Photolysis and Product I d e n t i f i c a t i o n . . 121 (d) S e n s i t i z e d Photolysis and Product I d e n t i f i c a t i o n 122 (e) D i s t r i b u t i o n of Products 123 4. Trans-3,4-dimethyl-3-acetyl-l-pyrazoline (99) 123 (a) Preparation and I d e n t i f i c a t i o n 123 (b) P y r o l y s i s and Product I d e n t i f i c a t i o n 124 (c) D i r e c t Photolysis and Product I d e n t i f i c a t i o n . . 126 (d) S e n s i t i z e d Photolysis and Product I d e n t i f i c a t i o n 126 (e) D i s t r i b u t i o n of Products 127 5. C i s - and Trans-3,5-dimethyl-3-acetyl-l-pyrazolines (19) and (20) 128 (a) Preparation 128 (b) S e n s i t i z e d Photolysis and Product I d e n t i f i c a t i o n 129 (c) D i s t r i b u t i o n of Products 130 6. (3S*,4S*,5R*)- and (3S*,4S*,5S*)-3,4-Dimethyl-3-acetyl-5-phenyl-l-pyrazolines (30) and (31) 130 (a) Preparation of Pyrazolines 130 - v i -Page (b) Di r e c t Photolysis and Product I d e n t i f i c a t i o n . . 131 (c) S e n s i t i z e d Photolysis and Product I d e n t i f i c a t i o n 133 (d) D i s t r i b u t i o n of Products 133 7. (3S*,4R,5R)- and (3S*,4R*,5S*)-3,4-Dimethyl-3-acetyl-5-phenyl-l-pyrazolines (32) and (33) 134 (a) Preparation of Pyrazolines 134 (b) Direct Photolysis and Product I d e n t i f i c a t i o n . . 135 (c) S e n s i t i z e d Photolysis and Product I d e n t i f i c a t i o n 135 (d) D i s t r i b u t i o n of Products 136 8. (3S*,4S*,5S*)- and (3S*,4S*,5R*)-3,5-Dimethyl-3-acetyl-4-phenyl-l-pyrazolines (34) and (35) 136 (a) Preparation of Pyrazolines 136 (b) D i r e c t Photolysis and Product I d e n t i f i c a t i o n . 137 (c) S e n s i t i z e d Photolysis and Product I d e n t i f i c a t i o n 138 (d) D i s t r i b u t i o n of Products 139 9. Photolysis of Pyrazolines 140 (a) Method for Direct Photolysis 140 (b) Method f o r S e n s i t i z e d Photolysis 141 10. Control Experiments 143 (a) D i r e c t Photolysis 143 (b) Sen s i t i z e d Photolysis 144 11. Relative Rates f o r the Thermal Decomposition of Pyrazolines 145 (a) Relative Rates of Pyrazolines 30. a n c * 21. (b) Relative Rates of Pyrazolines _3_2 and _33 147 (c) Relative Rates of Pyrazolines and 3_5 147 - v i i -Page 12. Nuclear Overhauser E f f e c t s 148 (a) General Experimental Procedure 148 (b) Preparation of Pyrazoline 34 and Dihydrofuran 96 f o r N.O.E. Studies 149 (c) N.O.E. Results 150 13. Rearrangement of Tetrasubstituted Cyclopropanes ... 150 (a) Experimental Conditions 150 (b) I d e n t i f i c a t i o n of Dihydrofurans 96_ and 97_ .... 151 (c) Thermal and Photochemical Results 153 (d) Control Runs 153 14. K i n e t i c Studies 156 (a) Experimental Conditions 156 (b) C i s - and Trans-l-acetyl-l-methyl-2-phenylcyclo-propane (132) and (133) 159 (c) 3-Methyl-5-phenyl-3- and 4-pentene-2-one 160 (d) 2,3-Dimethyl-5-phenyl-4,5-dihydrofuran (136) . 161 (e) Attempted K i n e t i c s of Cis-Trans Isomerization. 161 BIBLIOGRAPHY 163 APPENDIX I Derivation of Rate Constants f o r Eq. 62, Table XVII 168 II Derivation of Arrhenius Parameters E and log A ... j.69 I I I Arrhenius Plot f o r Eq. 62, Table XVII 170 IV Derivation of Difference i n Arrhenius Parameters E a • • and log A for Eq. 67, Table XXIII 171 V Arrhenius Plot for Eq. 67, Table XXIII 172 - v i i i -LIST OF TABLES Table Page I 1-Pyrazolines Prepared 32 II N.m.r. Data f o r Tetrasubstituted Pyrazolines 40 III Observed Nuclear Overhauser Enhancements 43 IV D i s t r i b u t i o n of Products from Pyrazolines 98_ and 99_. 51 V D i s t r i b u t i o n of Products from Pyrazolines 19_ and 20. 53 VI D i s t r i b u t i o n of Products from Pyrazolines 30_ to ^ 3.. 55 VII D i s t r i b u t i o n of Products from Pyrazolines j54_ and 35. 56 VIII N.m.r. Data f o r Tetrasubstituted Cyclopropanes 59 IX N.m.r. Data f o r 4,5-Dihydrofurans 62 X Thermolysis of the Cyclopropyl Ketone 36_ 66 XI Thermolysis of the Cyclopropyl Ketone 37_ at 283.5°C. 67 XII Thermolysis of the Cyclopropyl Ketone 38 at 283.5°C. 68 o XIII Photolysis of Cyclopropane 36_ at 3100 A 69 o XIV Photolysis of Cyclopropane _3_7 at 3100 A 70 o XV Photolysis of Cyclopropane ^8 at 3100 A 71 XVI Dependence of Volume to Sample Ratio 77 XVII A c t i v a t i o n Parameters for Cyclopropyl Ketone-Dihydrofuran Interconversion 78 XVIII Cyclopropane D i s t r i b u t i o n f o r the C i s - and Trans-3,4- and 3,5-Pyrazolines 85 XIX Cyclopropane D i s t r i b u t i o n s for Other Cis-Trans-3,4- and 3,5-Pyrazolines 87 XX D i s t r i b u t i o n of Cyclopropanes from Tetrasubstituted 1-Pyrazolines 92 - i x -Table P a S e XXI Results f o r Cyclopropyl Ketone-Dihydrofuran Conversion 97 XXII Allowed Stereochemical Pathways f o r the Concerted Cyclopropyl Ketone-Dihydrofuran Conversion 99 XXIII P y r o l y s i s of the Cyclopropyl Ketone 36 at D i f f e r e n t Temperatures 110 XXIV D i s t r i b u t i o n of Products from the Decomposition of cis_-3,4-dimethyl-3-acetyl-l-pyrazoline 123 XXV D i s t r i b u t i o n of Products from the Decomposition of trans-3,4-dimethyl-3-acetyl-l-pyrazoline 128 XXVI D i s t r i b u t i o n of Products from the S e n s i t i z e d Photolysis of Pyrazolines '19 and 20_ 130 XXVII D i s t r i b u t i o n of Products from the Photolysis of Pyrazolines 30_ and 31^  133 XXVIII D i s t r i b u t i o n of Products from the Photolysis of Pyrazolines _32 and \3_3_ 136 XXIX D i s t r i b u t i o n of Products from the Photolysis of Pyrazolines j34 and _3_5 139 XXX Experimental Conditions f o r the D i r e c t Photolysis of Pyrazolines 140 XXXI Experimental Conditions f o r the S e n s i t i z e d Photolysis of Pyrazolines 1^2 XXXII Experimental Data for D i r e c t Photolysis Control Experiments 1^3 XXXIII Experimental Data for S e n s i t i z e d Photolysis Control Experiments 145 - x -Table Page XXXIV Relative Rates of Decomposition of Pyrazolines 30_ and 31 146 XXXV Experimental Data f o r Thermal and Photochemical S t a b i l i t y of Dihydrof urans 96_ and 9_7 154 XXXVI Eq u i l i b r i u m P o s i t i o n s f o r Equation 70 157 - x i -LIST OF FIGURES Figure Page 1 P o s s i b l e intermediates formed by the thermal decomp-o s i t i o n of 3,4-dimethyl-3-carbomethoxy-l-pyrazolines 3 2 P o s s i b l e concerted mechanism f o r the p h o t o l y t i c decomposition of 3,4-dimethyl-3-carbomethoxy-l-pyrazolines 4 3 Step-wise mechanism i n v o l v i n g diazonium z w i t t e r i o n and diazonium d i r a d i c a l f o r the thermal decomposition of 3,5-dimethyl-3-carbomethoxy-l-pyrazolines 7 4 P o s s i b l e concerted mechanisms f o r the thermal decomposition of 3,5-dimethyl-3-carbomethoxy-l-pyrazolines 8 5 Step-wise mechanism i n v o l v i n g an antisymmetric t r i -methylene d i r a d i c a l f o r the thermal decomposition of 3,5-dimethyl-l-pyrazolines 9 2 2 6 [6 a + 6 s] Concerted mechanism f o r the e l i m i n a t i o n of nitrogen from a pyrazoline 11 7 Consideration of pos s i b l e routes f o r thermal decompo-s i t i o n of 4-methyl-l-pyrazoline and i t s 4-deuterio d e r i v a t i v e 12 8 Trimethylene intermediate from the thermal decompo-s i t i o n of 3-methyl-4-deuterio-l-pyrazolines 15 9 T r a n s i t i o n state f o r concerted e l i m i n a t i o n of from exo-5,6-dideuterio-2,3-diazobicyclo[2.2.l]-2-heptene 7^ - x i i -Figure Page 10 A l t e r n a t i v e diazonium d i r a d i c a l mechanism f o r nitrogen e l i m i n a t i o n from exo-5,6-dideuterio-2,3-diazobicyclo[2.2.1]-2-heptene 18 11 Pyramidal d i r a d i c a l mechanism f o r decomposition of exo- and endo-5-methoxy-2,3-diazobicyclo[2.2.1]-2-heptene 20 12 The trimethylene d i r a d i c a l (open chain) mechanism for c i s - t r a n s isomerization of cyclopropanes 23 13 Smith mechanism for c i s - t r a n s isomerization of cyclopropanes 24 14 The trimethylene d i r a d i c a l (ir-cyclopropane) mechanism for c i s - t r a n s isomerization of cyclopropanes 24 15 R a t i o n a l i z a t i o n of c i s - t r a n s isomerization of c y c l o -propanes using separate d i r a d i c a l s f o r each c y c l o -propane precursor 29 16 A v a i l a b l e conformations f or pyrazolines 0^_ and _31 .. 38 17 Concerted t r a n s o i d a l mechanism f o r the formation of o l e f i n s from pyrazolines bearing a C-3 e l e c t r o n withdrawing group 45 18 Decomposition routes a v a i l a b l e f o r t e t r a s u b s t i t u t e d 1-pyrazolines 81 19 Mechanism for reverse c y c l o a d d i t i o n r e a c t i o n f o r pyrazoline decomposition 33 20 Formation . of a dihydrofuran from pyrazolines 19_ and 20 84 - x i i i -Figure Page 21 D i r a d i c a l mechanism (of I n t e g r i t y ) f o r conversion of cyclopropyl ketones to dihydrofurans 104 22 D i r a d i c a l mechanism (of In t e g r i t y ) f o r the photo-chemical decomposition of t e t r a s u b s t i t u t e d 1-pyrazolines 106 23 D i r a d i c a l mechanism (of I n t e g r i t y ) f o r the interconver-s i o n of the cyclopropyl ketones 132 + 133 and dihydrofuran 136 114 - x i v -ACKNOWLEDGEMENT I wish to thank my d i r e c t o r of research, Dr. D.E. McGreer, f o r the many discussions about my research project and for the assistance i n w r i t i n g t h i s t h e s i s . I thank Miss P h y l l i s Watson and Mr. Roland Burton f o r the numerous n.m.r. spectra required f o r t h i s work, and I thank Mr. Peter Borda f or performing the elemental microanalyses. - 1 -•I. INTRODUCTION There are numerous examples in the literature concerning the formation and breaking of cyclopropane bonds. This thesis w i l l deal with three such aspects - the formation of cyclopropanes from pyrazolines, eq. 1; the geometrical cis-trans isomerization of cyclopropanes, eq. 2; and the formation of dihydrofurans from cyclo-propyl ketones, eq. 3. 0 - 2 -1. Cyclopropanes from 1-Pyrazolines (a) The Beginning of a Problem Although s e v e r a l reports appeared i n the literature"'" concerning the preparation arid decomposition of pyrazo l i n e s , Rinehart and Van Auken (la,b) were the f i r s t to present a s i g n i f i c a n t study dealing with stereochemical formation of cyclopropanes from 1-pyrazolines• Their study was involved with the thermal and d i r e c t p h o t o l y s i s of c i s - and trans-3,4-dimethy1-3-acetyl-1-pyrazolines-(1) and -(2) r e s p e c t i v e l y , eqns. 4 and 5. In both modes of decomposition, the formation of the A/2™3 VZV02™3 ° t -> + *"* N. ^ + X + * 3 4 CO CH — > 18 12 70 [4] I | 73 0 23 C0oCH_ 2 3 ^ [5] hv 28 35 37 2 87 11 cyclopropane products was observed to be s t e r e o s e l e c t i v e , with the d i r e c t p h o t o l y s i s being the more s t e r e o s e l e c t i v e of the two processes. Several mechanisms were presented by Rinehart and Van Auken (lb) which could accommodate t h e i r r e s u l t s . Intermediates such as the ^ reference (la,b) contains a l i s t of references p e r t a i n i n g to pyrazoline chemistry p r i o r to 1961. - 3 -diazonium ion 5_, the zw i t t e r i o n 6 ,^ or the s i n g l e t d i r a d i c a l 7_ (Figure 1) could be formed i n the thermal decomposition, and the loss of geometry could take place a f t e r t h e i r formation. The intermediate Figure 1. Possible intermediates formed by the thermal decomposition of 3,4-dimethyl-3-carbomethoxy-l-pyrazolines. 5 a l s o o f f e r s the p o s s i b i l i t y of displacement of the diazonium group by backside attack of the C-3 carbanion. In the case of the p h o t o l y t i c decomposition, concerted t r a n s i t i o n states 8^ and 9_ (Figure 2) are favoured owing to the high s t e r e o s e l e c t i v i t y of the process. I t was also f e l t that a s i n g l e t d i r a d i c a l species such as _7 (Figure 1) might be formed from the p h o t o l y s i s . Further work by Overberger and Anselme (2a,b) on the decomposition of 1-pyrazolines followed, i n which they reported the thermal and - 4 -2 9 4 Figure 2. Possible concerted mechanism for the photolytic decomposition of 3,4-dimethyl-3-carbomethoxy-l-pyrazolines. photolytic decomposition of trans-3,5-diphenyl-l-pyrazoline-(10) to be stereoselective i n both modes, eq. 6. Overberger et a l (2a) carried out electron spin studies of the photolytic decomposition of the trans-pyrazoline 10 at 77°K and their results indicated the presence of a free radical in each case. No evidence was found for a t r i p l e t state. This prompted a rationalization invoking a free radical mechanism, u t i l i z i n g a 1,3-diradical (similar to species J7, Figure 1) that rapidly couples. Overberger and co-workers (3a,b) have also prepared c i s - and trans-bis(p-methoxyphenyl)-1-pyrazolines-(11) and -(12) and reported their thermal and photolytic decomposition, eqs. 7 and 8. Both the cis and trans pyrazolines 11 and 12^  showed stereoselectivity upon - 5 -p h o t o l y s i s . However, the thermal r e s u l t s showed that the trans-pyrazoline gave the trans cyclopropane i n a h i g h l y s t e r e o s e l e c t i v e manner; whereas, the c i s - p y r a z o l i n e gave the trans cyclopropane as the major product. cis-cyclopropane trans-cyclopropane Ph \x''| I ~ A > 11 89 [6] Ph 10 p - A n i s y l A 6.7 93.3 [ 7 ] p - A n l s y l » = » 11 p - A n i s y l p - A n i s y l [8] '^ T^^ T^^ ' A > 43.0 57.0 N Z : N h v - d ^ 5 7 2 4 2 > 8 12 The r a t i o n a l i z a t i o n of Overberger and Anselme (2a) that a d i r a d i c a l i s generated both thermally and photochemically s t i l l accommodates t h e i r r e s u l t s , by using a d i r a d i c a l whose l i f e t i m e allows for r o t a t i o n competitive with r i n g closure, and thus some loss of s t e r e o s p e c i f i c i t y . This affords the opportunity of the d i r a d i c a l to proceed to an e q u i l i b r i u m mixture. At about the same time as Overberger and Anselme's work appeared (2a), McGreer et a l (4,5) published two reports concerning 1-pyrazolines - 6 -having an electron withdrawing group at C-3. In one case (5), pyrazolines were prepared showing the cis-trans relationship between C-3 and C-5. The most striking feature arising from the pyrolysis of cis and trans-3,5-dimethyl-3-carbomethoxy pyrazolines-(13) and -(14) respectively i s that trans-4 was the major cyclopropane from the c i s -pyrazoline; and in an analogous fashion, cis-3 was the predominant cyclopropane from the trans-pyrazoline, eqs. 9 and 10. The direct photolysis of the pyrazolines behaved in the usual manner - that i s , the reaction proceeded in a stereoselective manner. cis-cyclopropane trans-cyclopropane other [9] C02Me N m N cis-13 A-neat. hv-d 18 61 48 23 34 16 [10] C02Me A-neat N ZZZ N trans-14 hv-d 60 22 15 65 25 13 Choices of reaction paths used to explain the thermal decomposi-tion of the 1-pyrazolines Vi and 14_ become fewer because of the striking crossover of products. A diradical species along the lines of T_ (Figure 1) is not satisfactory because of the unusual crossover of stereochemistry in the products. McGreer et a l (5) agree that the diradical .16 or the dipolar species 15 (Figure 3) can explain their unusual results. The predominant inversion at C-3 or C-5 would occur - 7 -cis-3 Figure 3 . Stepwise mechanism involving diazonium zwitterion and diazonium diradical for the thermal decomposition of 3,5-dimethyl-3-carbomethoxy-l-pyrazolines. because of the stepwise loss of nitrogen from 15_ or 16^  owing to backside displacement by the C-3 carbanion or radical. McGreer et al (5), however, favoured a concerted process. Two extremes for nitrogen elimination are considered. The first (route I, Figure 4) is the loss of nitrogen in the same plane as C-3, C-4 and C-5 resulting in two p-orbitals orientated such that they couple to give a product of retained configuration. This process is identical to the one proposed for the photochemical reaction by Van Auken and Rinehart (lb) (see Figure 2). - 8 -The second extreme (route I I , Figure 4) involves l o s s of nitrogen perpendicular to C-3, C-4 and C-5 which would give two p - o r b i t a l s at C-3 and C-4 p a r a l l e l to each other, but i n order to accommodate the s t e r i c f a c t o r there would be twisting of the molecule to r e l i e v e t h i s s t r a i n so as to lead to in v e r s i o n at one of the centers. C0 2CH 3 4_ I / / N ^ N 14 route I trans-14 route ^ XT C0 2CH 3 14 C0 2CH 3 C » C H 3 C0 2CH 3 CH, 18 <5 C0 2CH 3 trans-4 c i s - 3 C0 2CH 3 Figure 4. Possible concerted mechanisms f o r the thermal decomposition of 3,5-dimethy1-3-carbomethoxy-l-pyrazolines. Si m i l a r r e s u l t s were obtained by McGreer et a l (4) f o r c i s - and trans-3,5-dimethyl-3-acetyl-l-pyrazolines-(19) and -(20) r e s p e c t i v e l y . That i s , there was the curious crossover of stereochemistry i n the thermal decomposition, while the d i r e c t photolysis gave predominantly cyclopropanes having the same stereochemistry as the s t a r t i n g p yrazolines. - 9 -(b) A d d i t i o n a l Pyrazoline Decompositions Another cl a s s of pyrazolines, those bearing only a l k y l substituents, has been extensively i n v e s t i g a t e d by Crawford and co-workers. Two such pyrazolines prepared by Crawford et a l (6a,b,c) were c i s - and trans-3,5-dimethyl-l-pyrazolines-(21) and -(22) r e s p e c t i v e l y . Like the isomeric 3,5-substituted pyrazolines studied by McGreer and co-workers (4,5), a r e v e r s a l of stereochemistry occurred during the gas phase p y r o l y s i s (6c), eqs. 11 and 12. I t was suggested by the authors (6c) that a trimethylene d i r a d i c a l species such as 2_3 or 24 (Figure 5) e x i s t s as a s i n g l e t i n which both electrons are i n an Figure 5. Stepwise mechanism i n v o l v i n g an antisymmetric trimethylene d i r a d i c a l f o r the thermal decomposition of 3,5-dimethyl-1-pyrazolines. - 10 -antisymmetric or b i t a l . Subsequent preferred conrotation and closure to a cyclopropane nicely explains their experimental results. The suggestion of such a species as 23 of 2h_ might exist originates from the theoretical work of Hoffman (7) whose extended Huckel calculations of the potential surface of trimethylene showed a minima at a point where the C-3, C-4, C-5 bond angle is roughly 125° and whose terminal methylene groups l i e i n the same plane as the carbon atoms. [11] N N cis-21 [12] N — N trans-22 x I 1 h v-gas cis-26 _ ' trans-25 A-gas > 33.2 66.1 0,7 hv-gajs 47.1 42.5 10.4 hv-Et^H 33.9 61.7 4.4 A-gas^ 72.6 25.4 2.0 59.5 26.7 13.8 hv-EtOH 44.5 45.6 9.1 The photolysis of pyrazolines 21 and 22^  gave results which are d i f f i c u l t to explain (8b). In the gas phase,the tfans-pyrazoline exhibits the same stereoselectivity as the thermal process while the cis-pyrazoline exhibits the opposite behaviour. On the other hand, i n the l i q u i d phase, the tfans-pyrazoline now exhibits the opposite behaviour and the cis-pyrazoline behaves similarly to the thermal - 11 -decomposition. In general, the conrotation process does not appear to be such an important pathway i n the p h o t o l y t i c decomposition as i n the thermal decomposition. More recent l y , Bergman (9c) have considered the p o s s i b i l i t y that the expulsion of nitrogen from a pyrazoline i s the microscopic reverse of a h y p o t h e t i c a l 2 + 2 c y c l o a d d i t i o n of to a cyclopropane C-C bond. The reaction i s an allowed [,2 + ,2 ] process, whose t r a n s i t i o n 6 a 6 s Y ' state i s h i g h l y s t r a i n e d (Figure 6). This explanation would n i c e l y e x p lain the crossover of stereochemistry i n the thermal decomposition of 3,5-substituted pyrazolines (4,5,6c). R H trans-pyrazoline cis-cyclopropane Figure 6. 2^ + g2 g] Concerted mechanism f o r e l i m i n a t i o n of nitrogen from a pyrazoline. Crawford and co-workers have prepared s e v e r a l a l k y l s u bstituted 1-pyrazolines incorporating deuterium and the r e s u l t s have been used to probe the stereochemistry and to determine deuterium k i n e t i c isotope e f f e c t s . In the case of pyrazolines 2j5 and 29^  (6a,b) (Figure 7), a k i n e t i c isotope e f f e c t of 1.07 was observed. Two mechanisms were considered - one i n which a common intermediate was formed; and two, one i n which o l e f i n and cyclopropane formation occurred by separate pathways. - 12 -C H 3 H,(D) mechanism I N z = N 28,(29) nitrogen free intermediate o l e f i n cyclopropane CRo H,(D) mechanism I I N ~ N 28,(29) o l e f i n cyclopropane 'Figure 7. Consideration of p o s s i b l e routes f o r thermal decomposition of 4-methyl-l-pyrazoline and i t s 4-deuterio d e r i v a t i v e . In mechanism I, assuming no isotope e f f e c t f o r the cyclopropane forming r e a c t i o n , an isotope e f f e c t of 1.80 can be c a l c u l a t e d f o r the o l e f i n forming r e a c t i o n , a value which i s close to that observed f o r the isomerization of deuterated cyclopropanes (14a,b). On the other hand, mechanism I I leads to an isotope e f f e c t of 1.50 f o r the o l e f i n forming r e a c t i o n and a value of 0.84 f o r the c y c l o -propane formation. The value of 0.84 implies that tie s u b s t i t u t i o n of deuterium at C-4 increases the cyclopropane formation by 19%, thus i n d i c a t i n g scheme I I to be hig h l y improbable. The conclusion i s that during the rate determining step a nitrogen-free intermediate i s formed which i s common to both the o l e f i n and cyclopropane formation. - 13 -A recent study by McGreer et a l (15), i n v o l v i n g the thermal decomposition of 1-pyrazolines uniquely substituted at a l l three carbons, o f f e r e d the opportunity of d i s t i n g u i s h i n g between i n v e r s i o n or retention at C-3 and C-5 as the pyrazoline proceeds toward a cyclopropane product. I t i s noteworthy that the three pyrazolines _30_, _32_ and 34_, tfiich have three substituents pseudo e q u a t o r i a l and one substituent pseudo a x i a l , decompose thermally to give as the major cyclopropane the one having the same stereochemistry as the s t a r t i n g p yrazoline, eqs. 13-15. On the other hand, the C-5 epimeric pyrazolines J^L, _33, and 35 decompose thermally to give a more random display of cyclopropane products, eq. 16. 98% 30 37 91% 32 36 COCH COCH 3 79% 34 36 - 14 -COCH3 COCH 3 N random mixture [16] " / / ^ of cyclopropanes 31 33 35 The r e s u l t s were explained by proposing that s t e r i c and substituent factors i n the i n i t i a l pyrazoline can force the r e s u l t i n g three carbonT T-cyclopropane to act e i t h e r as a symmetric or as an a n t i -symmetric u n i t . C a l c u l a t i o n s have been c a r r i e d out by Hoffman (7) that suggests at small c e n t r a l angles of l e s s than 100° the symmetric species i s more stable while at angles of greater than 100° the antisymmetric form becomes more s t a b l e . Evidence was presented (15) that there was a larger degree of f o l d i n g between the two planes defined by C-3, C-4, C-5, and N-1, N-2, C-3, C-5 i n the pyrazolines _30, 32., and J34_ than i n the C-5 epimers 31, 3_3, and 35. I t i s t h i s degree of f o l d i n g that can change the C-3, C-4, C-5 angle and therefore the r e s u l t i n g trimethylene d i r a d i c a l can be forced to act e i t h e r as an antisymmetric or symmetric u n i t . Further evidence was presented by Crawford and Erikson (10) to give support for a nitrogen-free intermediate from the p y r o l y s i s of a l k y l - l - p y r a z o l i n e s . C i s - and trans-4-deuterio-3-methyl-l-pyrazolines 40 and 4JL r e s p e c t i v e l y were chosen since both pyrazolines are capable of producing the same intermediate hl_ (Figure 8). I f t h i s intermediate - 15 -has s u f f i c i e n t time to become completely free of the nitrogen produced, then the product r a t i o s w i l l be i d e n t i c a l and independent of i n i t i a l stereochemistry. This expectation was r e a l i z e d by the complete analysis of the product r a t i o s which were almost i d e n t i c a l from both pyrazolines. D •> o l e f i n s plus cycloprop 41 Figure 8. Trimethylene intermediate from the thermal decomposition of 3-methyl-4-deuterio-l-pyrazolines. Secondary deuterium k i n e t i c isotope e f f e c t s from the thermolysis of 1-pyrazolines have given a d d i t i o n a l support f o r a trimethylene intermediate. K i n e t i c isotope e f f e c t s of 1.19 and 1.21 were found f o r the 5,5-d 2 analogues 4_3 and 44_ of c i s - and trans-3,4-dimethy1-1-pyrazolines-(69) and -(70) r e s p e c t i v e l y , implying that the C-5 N-1 bond i s breaking i n the rate determining t r a n s i t i o n state (11). - 16 -Further k i n e t i c isotope e f f e c t s were furnished by Crawford and Al-Sader (13) by studying the rates and product r a t i o s of a s e r i e s of deuterated d e r i v a t i v e s of the parent 1-pyrazoline 45. cyclopropane propylene k^/k^ [17] [18] N — N 45 N ZZZ N 46 88.43 87.99 11.57 12.01 1.19 [19] [20] [21] 48 n N N 49 87.43 89.21 90.27 12.57 10.79 9.73 1.40 1.05 1.12 Comparison of the rates f o r pyrazolines 45_, 4_6_, and 47 confirms that both C-N bonds are breaking i n the rate-determining step, eqs. 17, 18, 19. Complete analysis of the e f f e c t of deuterium on the product r a t i o s was found to be e n t i r e l y consistent with a nitrogen free intermediate. McGreer and Masters (16) have studied the 5,5-d2 d e r i v a t i v e 50 of 3-methyl-3-carbomethoxy-l-pyrazoline-(51) and the 5,5-d 2 d e r i v a t i v e _52^  of 3-methyl-3-cyano-l-pyrazoline-(53) . K i n e t i c isotope e f f e c t s of 1.22 and 1.23 were observed r e s p e c t i v e l y , providing evidence for the breaking of the C-5 N-1 bond i n the rate determining step. (c) B i c y c l i c Pyrazolines The decomposition of b i c y c l i c pyrazolines o f f e r s t i l l more unusual r e s u l t s . Roth and Martin (17a,b) reported that the thermolysis of exo-5,6-d 2-54 gave mainly a product of double i n v e r s i o n . These authors a t t r i b u t e d the predominance of double i n v e r s i o n to a concerted e l i m i n a t i o n of nitrogen with accompanying backside p - o r b i t a l overlap i n the t r a n s i t i o n state 57_ (Figure 9). exo-54 Figure 9. T r a n s i t i o n state for concerted e l i m i n a t i o n of from exo-5,6-dideuterio-2,3-diazobicyclo[2.2.l]-2-ketone. An a l t e r n a t i v e scheme proposed (17b) to explain t h e i r r e s u l t s i s based on the a d d i t i o n of a dienophile to bicyclopentane, a reaction which proceeds by double i n v e r s i o n , eq. 22. A reverse mechanism was - 18 -t h e r e f o r e proposed as a p o s s i b i l i t y f o r the decomposition of 54. 55 62 55 Fig u r e 10. A l t e r n a t i v e diazonium d i r a d i c a l mechanism f o r n i t r o g e n e l i m i n a t i o n from e x o - 5 , 6 - d i d e u t e r i o - 2 , 3 - d i a z o b i c y c l o -[2„2.1]-2-heptene. An analogous o b s e r v a t i o n of double i n v e r s i o n f o l l o w e d by A l l r e d and Smith (18a,b) eqs. 23,24. Instead of using e i t h e r of Roth and Ma r t i n ' s r a t i o n a l i z a t i o n s (17a,b), they chose to explain t h e i r r e s u l t s by i n v o k i n g a pyramidal d i r a d i c a l . - 19 -65 66 [23] CH„0 N 37 63 exc—63 [24] N 6 94 CH o0 endo-64 Their mechanism proposes that s t r u c t u r a l l y inverted pyramidal d i r a d i c a l s 67a and 67b (Figure 11) a r i s e d i r e c t l y from the e l i m i n a t i o n of N 2 from 63^  and £>4_ r e s p e c t i v e l y . This i n v e r s i o n i s thought to be a consequence of r e c o i l released by C-N bond breaking. The excess of inverted structure i n d i c a t e s that r i n g closure occurs before 67a or 67b can f u l l y e q u i l i b r a t e . The idea of a pyramidal d i r a d i c a l has been u t i l i z e d by Crawford and Mishra (19) to explain part of t h e i r r e s u l t s from the decomposition of (3R;5R)-(+)-trans-3,5-dimethyl-l-pyrazoline-(22). On thermolysis, t h i s pyrazoline gave 25.6% of trans-1,2-dimethyl cyclopropane of 23% o p t i c a l p u r i t y having the S:S c o n f i g u r a t i o n , eq. 25. This r e s u l t - 20 -CH V / N CH exo-63 67-a I CH 3 0 65 N J endo-64 1 CH 3 0 67-b CH 3 0 66 Figure 11. Pyramidal d i r a d i c a l mechanism f o r decomposition of exo-and endo-5-methoxy-2,3-diazobicyclo-[2.2.l]-2-heptene. i n d i c a t e s an excess of double i n v e r s i o n , and i n order to account for t h i s observation, use i s made of an inverted pyramidal d i r a d i c a l intermediate. - 21 -[25] 3R:5R-22 , 26 R:R-25 S:S-25 73% 25% (23% optical purity of S:S configuration) (d) Triplet Sensitization Stereochemical studies involving t r i p l e t sensitization of 1-pyrazolines have drawn considerably less attention than the thermolysis or direct photolysis, and consequently experimental data are lacking. A l l of the examples to date have dealt with pyrazolines that can give only two isomeric cyclopropanes, and thus a single rotation can interconvert the two products. However, two clear results have been shown from t r i p l e t sensitiza-tion. The f i r s t result i s that, in general, there i s a reduction i n the amount of ol e f i n formation. What small amount of ol e f i n that i s formed may be due to a slight amount of direct photolysis taking place. It would appear that the t r i p l e t diradical cannot produce olefins directly, and that even after spin inversion occurs, the resulting intermediate closes almost exclusively to cyclopropanes (8). The second result i s that the product ratios from any two isomeric pyrazolines are approaching each other. In the case of the alkyl 1-pyrazolines 69 and 10_ the ratio is almost identical; and likewise, the ratios from 21^  and 22 are nearly equal (8a,b), eqs. 26 to 29. - 22 -For the 3-carbotnethoxy pyrazolines 7_1 and J72_ i t would appear that e q u i l i b r a t i o n of the intermediate cannot be reached as e a s i l y (20) as for the a l k y l s u b s t i t u t e d 1-pyrazolines, eqs. 30 and 31. % cis-A % trans-A trans-A/cis-A [26] [27] [28] N N cis-69 N N trans-70 N = N cis-21 26.8 26.2 38.9 70.6 72.0 60.1 2.63 2.77 1.55 [29] N = N trans-22 38.8 61.2 1.58 [30] ''C02Me 95 ,053 [31] '6o2Me 86 14 ,163 - 23 -2. Cis-Trans Isomerization of Cyclopropanes There are several choices of mechanisms which have gained noticeable attention since 1958 when Rabinovitch et a l (24a) reported the geometrical and structural Isomerization of cyclopropane-d^-73. The mechanism (Figure 12) that these authors considered most reasonable for cis-trans isomerization involved ring rupture to an open chain - that i s , the formation of a trimethylene diradical whose bond rotations are fast relative to cyclization. This trimethylene diradical may also proceed to propylene by structural isomerization. This 1,3-trimethylene diradical has been frequently suggested as an intermediate i n later studies (25a,b) concerning geometric and structural isomerization of cyclopropanes. Figure 12c The trimethylene diradical (open chain) mechanism for cis-trans isomerization of cyclopropanes. The second theory of concern was presented by Smith (26) as an alternative explanation for the experimental results of Rabinovitch et a l . (24a), Smith preferred a simple interpretation using a species (Figure 13) i n which there i s p a r t i a l hydrogen migration without ring opening. This places the 5 atoms approximately i n a co-planar transition - 24 -state i n which the methylene group may rotate e i t h e r of two ways i n returning to a ground state cyclopropane. '/D 74 Figure 13. Smith mechanism f o r c i s - t r a n s isomerization of c y c l o -propanes. A t h i r d theory has been developed more recently by Hoffman (7) who suggests that the 1,3-trimethylene d i r a d i c a l often proposed as an intermediate may be a planar species, a n-cyclopropane (Figure 14) with an antisymmetric non-bonding molecular o r b i t a l that undergoes a conrotation process. This theory has gained i n d i r e c t support from the decompositions of 3,5-disubstituted-l-pyrazolines i n which the s t r i k i n g crossover of stereochemistry was observed i n the thermal Z l 74 Figure 14. The trimethylene d i r a d i c a l (u-cyclopropane) mechanism f o r ci s - t r a n s isomerization of cyclopropanes. - 25 -decomposition (4-6). Moreover, crossover of stereochemistry has been noted i n the photochemical decarbonylation of cis and trans-2,4-dimethylcyclobutane (27). In addition, c i s - and trans-2,4-dimethyl sulfones gives cyclopropanes with net crossover of stereochemistry (28). S e v e r a l studies have been conducted on various cis-trans isomeric cyclopropanes. In one, already mentioned, Rabinovitch et a l (24a) studied the kinetics of the thermal isomerization of cis-cyclopropane-d^-(73) and they found that i t underwent cis-trans isomerization faster t h a n i t isomerized to propene-d~, eq. 32. [32] The cis-trans isomerization (29a,b) and the structural isomeriza-tion of cis-l >2-dimethylcyclopropane have been studied. The addition of the two methyls lowers the activation energy of cis-trans isomeriza-tion by 5.7 kcal/mole and the structural isomerization by about 4 kcal/ mole. Again, the geometric isomerization i s faster than the structural rearrangement. Similar activation parameters were obtained for the geometrical isomerization of l-ethyl-2-methylcyclopropane (29c). Studies performed on vinylcyclopropane-(77) (30a,b) and on l-deuterio-2-vinylcyclopropane-(75) (31) have led to some interesting discussions, eqs. 33 to 35. The presence of the vinyl group has further reduced the activation energies of both processes, with the reduction i n - 26 -the a c t i v a t i o n energy being much more f o r c i s - t r a n s isomerization f o r the s t r u c t u r a l rearrangement. [33] [34] -47,100/RT 4 9 , 7 0 0 / R T 77 78 [35] = 53.6 to 57.3 7 7 log A = 13.0 to 14.4 The vinylcyclopropane to cyclopentene rearrangement, eq. 34, represents a 15.4 kcal/mole decrease f o r the cleavage of a C-C cyclopropane bond as opposed to the c i s - t r a n s isomerization of 1,2-dideuteriocyclopropane, eq. 32. This decrease has been a t t r i b u t e d to the a l l y l i c s t a b i l i z a t i o n of the developing d i r a d i c a l intermediate (25a, 30a,b, 32a,b). On the other hand, t h i s s u b s t a n t i a l decrease can also be accounted f o r by invoking a concerted mechanism (31,33a,b,c). The energies of a c t i v a t i o n have been obtained f o r a s e r i e s of 1,2-diarylcyclopropanes by Rodenwald and DePuy (34). The c i s - t r a n s isomerization f o r t h i s s e r i e s of compounds has been reduced from 65.1 kcal/mole f o r cyclopropane-d,,-73 to 33.5 kcal/mole for c i s - d i p h e n y l -cyclopropane-79, a d i f f e r e n c e of about 30 kcal/mole. This lowering - 27 -of the energy b a r r i e r was considered by these authors to be a r e f l e c t i o n of the s t a b i l i z a t i o n of the d i r a d i c a l intermediate by the two phenyl groups. An i n t e r e s t i n g aspect of t h i s s e r i e s of cyclopropanes i s the t o t a l lack of any s t r u c t u r a l isomerization. CfiH ,, n -33,500/RT [36] / \ ^ = / — V k x = 1 0 1 1 * 2 e C 6 H 5 C 6 H 5 1 0 _ -36,400/Rt [37] / - A ^ / — V k 2 = I O 1 2 * 5 e p-Cl-C 6H 4 C 6H 4-p-Cl P-C1-C 6H 4 81 82 . C,H,-p-Cl A 3 ^ A / 12 s "36,800/RT ^ LIy k 3 = I O 1 2 ' 5 e C,HC C,H.-p-Cl C,HC 6 5 6 4 c 6 5 83 84 Attempts have been made to i n v e s t i g a t e the c i s - t r a n s isomerization of cyclopropanes by obtaining both the geometrical and racemization rates of o p t i c a l l y a c t i v e cyclopropanes. I t was hoped that the value of k /k could help decide which of the three mechanisms discussed rac tc r thus f a r plays an important r o l e . The f i r s t such example was due to Crawford and Lynch (35) who used trans-(-)-1,2-diphenylcyclo-propane-(80). They concluded that since racemization took place f a s t e r than t r a n s - c i s isomerization (k /k = 1.42), that a rac tc ' trimethylene species i s suggested and that the Smith mechanism alone - 28 -cannot account for the results. Two additional reports followed on the isomerization of optically active cyclopropanes. In one, Berson and Baliquist (36) synthesized an optical isomer of tetramethylcyclopropane-d^-85_. These authors concluded that neither a randomized intermediate (the open chain trimethylene diradical) nor an in-place rotation (Smith mechanism) can be the sole process. Furthermore, they concluded that a planar intermediate (n-cyclopropane trimethylene diradical) at most plays only a minor role. Similar conclusions have been reached by Carter and Bergman (9a,c) i n a similar study on optically active isomers of c i s -and tfans-l-methyl-2-ethylcyclopropanes (Figure 16). Bersori et a l (36) and Bergman et a l (9a,c) did however, propose a inechanism to explain their results. Their mechanism provides for a different diradical precursor for each cyclopropane product. These diradicals can undergo conversion to one another by means of one single rotation at a time. Their rationalization has the merit in that rotation rates and.cyclization rates can be adjusted to agree with the phenomeological rate constant. This mechanism does not require the precise nature of the diradicals as long as they retain some of the integrity of the cyclopropane precursor after formation. The system used by Berson et a l (36) is used to i l l u s t r a t e this mechanism (Figure 16). - 29 -Figure 15. R a t i o n a l i z a t i o n of c i s - t r a n s isomerization of cyclopropanes using separate d i r a d i c a l s f o r each cyclopropane precursor. 3. Cyclopropyl Ketone and Dihydrofuran Interconversion Unlike the conversion of vinylcyclopropanes to cyclopentene d e r i v a t i v e s (30-33) there are r e l a t i v e l y l i t t l e experimental data dealing with the conversion of a cyclopropyl aldehyde or ketone to a dihydrofuran. At any rate, an analogous s i t u a t i o n w i l l no doubt e x i s t i n which there i s the b a s i c argument f o r and against two d i s t i n c t l y d i f f e r e n t mechanisms - that i s , concerted versus stepwise."'" ^ For a b r i e f d iscussion on this point see the previous s e c t i o n dealing with the c i s - t r a n s isomerization of cyclopropanes. - 30 -There are several ways i n which a cyclopropyl ketone may be converted to a dihydrofuran. The f i r s t example was reported by Wilson (37a) on the interconversion of cyclopropane aldehyde 87_ and the 4,5-dihydrofuran-88, eq. 39. Other thermal examples have followed (37b,c). Dauben et a l (38) have reported the only photochemical conversion, eq. 40. In a d d i t i o n both acid c a t a l y s t s (39a,b) and base c a t a l y s t s C40a,b) promote such a r e a c t i o n , eqs. 41 and 42. Moreover, a novel bromine catalyzed rearrangement of cyclopropyl ketones to dihydrofurans has been r e a l i z e d i n t h i s laboratory (41), eq. 43. [39] [40] [41] [42] [43] (3:97) - 31 -4. Purpose of Present Research Cyclopropane formation from the d i r e c t and s e n s i t i z e d p h o t o l y s i s of 1-pyrazolines i s in v e s t i g a t e d by the preparation of a s e r i e s of t e t r a s u b s t i t u t e d pyrazolines uniquely s u b s t i t u t e d at a l l three ring carbons, These pyrazolines have the advantage that they can decompose to four isomeric cyclopropanes, and thus information can be obtained about the degree of retention or i n v e r s i o n at both C-3 and C-5 of the s t a r t i n g p yrazoline. The formation of dihydrofurans from cyclopropyl ketones i s approached by using cyclopropanes that are uniquely s u b s t i t u t e d at a l l three ring carbons and thus information about the stereochemical pathway can be found f o r t h i s conversion. Moreover, the reaction i s inv e s t i g a t e d both thermally and photochemically and therefore comple-mentary r e s u l t s can be obtained about the two modes of re a c t i o n . In addi t i o n , the cyclopropyl ketone - dihydrofuran interconversion i s studied k i n e t i c a l l y . At the same time, the above approach to the formation of c y c l o -propanes from pyrazolines and to the formation of dihydrofurans from pyrazolines enables some information to be derived about the c i s - t r a n s isomerization of isomeric cyclopropanes. I I . RESULTS 1. Preparation and I d e n t i f i c a t i o n of Pyrazolines The 1-pyrazolines prepared f o r the present work are l i s t e d i n Table I. The pyrazolines were prepared by the addition of diazo-methane, diazoethane, or phenyldiazomethane to the appropriate a,B-unsaturated ketone. TABLE I 1-Pyrazolines Prepared 1-Pyrazoline R, R, R. 98 99_ 19 20 30 H CH, H H H CH, H H H CH, H H H C H , C 6 H 5 H H CH, H H - 33 -31 32 33 34 35 H CH, CH, H H CH, H H C 6 H 5 C 6 H 5 H C 6 H 5 H CH3 H C 6 H 5 H C 6 H 5 H CH„ The mechanism of the 1,3-dipolar addition of a diazoalkane to an a f6-unsaturated ketone i s considered by Huisgen and co-workers (42a,b) to be a one step multi-center addition as opposed to a two step ionic mechanism. The concerted mechanism i s supported on two points. The f i r s t i s that the rate constants were measured for the addition of diazoalkanes to olefins to form pyrazolines (42a). The findings demonstrated that the rate constants were largely independent of the solvent used, that the rate constants were influenced substan-t i a l l y by ste r i c effects, and that the entropies of activation were both large and negative. Secondly, the reaction of diazomethane with c i s - and trans-olefins produced pyrazolines by a stereospecific pathway (42b). Thus, the stereochemistry of the starting olefin i s preserved in the 3,4-bond of the resulting pyrazoline. The preparation of pyrazolines and 99_ was accomplished by the addition of diazomethane to an ethereal solution of 3-methyl-3-pentene-2-one, (E)-(IOO) and (Z)-(IQO) respectively, eqs. 44 and 45. Evaporation of the ether followed by bulb to bulb vacuum d i s t i l l a t i o n gave the pyrazolines as clear colourless liquids. - 34 -The c i s - and trans-pyrazolines 98 and 99_ had i . r . absorptions at 1542 and 1546 cm ^ r e s p e c t i v e l y , t y p i c a l of a -N=N- s t r e t c h i n g mode (lb,2a,6b). The pyrazolines "98_ and 99_ had absorptions i n the u.v. spectrum (EtOH) at X = 336 my, E = 271 and X = 341, E = 245 r max max ' * r e s p e c t i v e l y , i n d i c a t i v e of the n - i r t r a n s i t i o n of the azo chromophore (lb,2a,6b). The n.m.r. spectra of the pyrazolines displayed the expected pattern with respect to both the chemical s h i f t p o s i t i o n s and the m u l t i p l i c i t y of each resonance. Assignment of stereochemistry to the pyrazolines 9_8_ and 9_9 was based on the accepted mechanism of Huisgen and co-workers (42a,b). In a d d i t i o n , the r e l a t i v e p o s i t i o n s of the chemical s h i f t s f o r the C-3 methyl and a c e t y l methyl were consistent with the a n i s o t r o p i c e f f e c t of the -N=N- double bond. This point i s discussed i n fu r t h e r d e t a i l with regard to the i d e n t i f i c a t i o n of the t e t r a s u b s t i t u t e d pyrazolines 310 - 35 -to 35_ The preparation of pyrazolines 19_ and 20_ was done according to the procedure of McGreer et a l (15). To an ethereal s o l u t i o n of f r e s h l y d i s t i l l e d methyl isopropenyl ketone-(lCT) was added diazoethane, eq. 46. Vacuum d i s t i l l a t i o n gave the pyrazolines _19_:^ P_ l n a r a t i ° °f 2:3. Two spinning band d i s t i l l a t i o n s gave the low b o i l i n g c i s - p y r a z o l i n e 19 and the high b o i l i n g trans-pyrazoline 20 i n r a t i o s of 80:20 and 5:95. [46] The pyrazolines 19_ and 20_ have previously been i d e n t i f i e d , with the assignment of stereochemistry based on the n.m.r. spectra (4). Addition of phenyldiazomethane to 3-methyl-3-pentene-2-one,(E)-(100) gave the pyrazolines 30_ and 31_ i n a r a t i o of 63:37 (15), eq. 47. P u r i f i c a t i o n by column chromatography gave the C-5 isomeric pyrazolines as a c l e a r c o l o u r l e s s l i q u i d . Two f r a c t i o n s , i n which the r a t i o of 30:31 was 69:31 and 62:38 were used f or the photolysis experiments. [47] - 36 -In order to increase the proportion of ^ 31 i n the mixture, advantage was taken of the fact that 30 thermally decomposes about 9 times faster than does pyrazoline 3i_ (see results at end of this section for further details). Thus by refluxing a portion of the crude reaction mixture in acetone for 23 hours, followed twice by column chromatography, there resulted a fraction of the pyrazolines 30 and _31 i n a ratio of 5:95 respectively. This fraction was also used i n the photolysis experiments. Addition of phenyl diazomethane to 3-methyl-3-pentene-2-one, (Z)-(IOO) gave the pyrazolines 32 and 33 in a ratio of about 2:1 respectively (15), eq. 48. Purification by column chromatography followed by recrystallization gave two samples of 2I2_ and _33 i n ratios of 40:60 and 80:20 respectively. These fractions were used i n the photolysis experiments. COCH [48] e,HcCHN0 •+ \ = / 03 2 \ 2-100 Three successive treatment of 4-phenyl-3-butene-2-one, (E)-(102) with diazoethane gave the pyrazolines 3>4_ and _35 i n a ratio of about 9:1 respectively (15), eq. 49. The major product 34 was crystallized out of solution. The mother liquor was chromatographed to give a fraction containing the pyrazolines _34_ and 35_ in a 45:55 ratio respectively. - 37 -[49] C 6H 5 : E-102 34 35 I t should be noted that although the stereochemistry about the 3,4-bond of the pyrazolines 30_ to 35_ i s known to be the same as the s t a r t i n g a,8-unsaturated ketone (42a,b), there remains the problem of d i s t i n g u i s h i n g between the C-3 epimers as a r e s u l t of the a d d i t i o n of diazoethane or phenyl diazoethane to the o l e f i n , eqs. 47 to 49. In view of the importance of correct assignment of stereochemistry to the pyrazolines and cyclopropanes, i t seems worthwhile to b r i e f l y review the fact s already known (15) and to discuss f u r t h e r data which contribute a d d i t i o n a l information. One important aspect that w i l l be used i n the following d i s c u s s i o n dealing with the assignment of stereochemistry to the C-5 epimeric pyrazolines i s the aspect of preferred conformation. The structure of a 1-pyrazoline i s considered to be a folded molecule i n which the planes defined by C-3, C-4, C-5, and N-1, N-2, C - l , C-2 create an angle of roughly 25° (4,6b,43). Thus, there are two a v a i l a b l e conformations to consider f o r every p y r a z o l i n e . Pyrazolines _30_ and _31_ w i l l be used to i l l u s t r a t e t h i s point (Figure 16). In order to decide which conformation of a pyrazoline w i l l predominate, consideration i s given to the e f f e c t of substituents. Studies have shown that substituents p r e f e r to occupy pseudo-equatorial p o s i t i o n s (4,5). Preference for a substituent to occupy a pseudo-equatorial - 38 -Figure 16. A v a i l a b l e conformations f o r pyrazolines 30_ and 31. p o s i t i o n i s strongest i n the case of c i s - 3 , 5 - d i s u b s t i t u t e d - l -pyrazolines so that the non-bonded d i a x i a l i n t e r a c t i o n i s avoided. For pyrazoline 30, conformation "a" w i l l be preferred to "b" since the former has three substituents pseudo-equatorial and only one pseudo-axial. On the other hand, 30-b places three of i t s substituents pseudo-axial and only one pseudo-equatorial. In ad d i t i o n , conformer "b" has a highly unfavourable non-bonded i n t e r -a c t i o n (the C-3 a c e t y l and C-5 phenyl). In the case of pyrazoline 31^ , however, both conformers place two substituents each i n a pseudo-axial and pseudo-equatorial environment. The conformer 31-b does, however, have the disadvantage - 39 -of a non-bonded interaction across C-3 and C-5 (the C-3 methyl and C-5 phenyl). Hence, i n both pyrazolines 30 and 31, the "a" conformations w i l l predominate. A second important aspect to consider i s the anisotropic effect of the -N=N- double bond on the chemical shifts of substituents i n the nuclear magnetic resonance spectra. The anisotropic effect of the -N=N- double bond has been commented on by several authors (4,6b,44a,b). In brief, the pseudo-axial position l i e s i n a shielding zone and thus a shift upfield i s expected; whe reas, the pseudo—equatorial position l i e s i n a deshielding zone and i s shifted downfield. Equipped with the knowledge of which conformer i s preferred i n a pyrazoline,coupled with the anisotropic shielding effect of the -N=N- double bond, a clear assignment of stereochemistry to epimeric C-5 pyrazolines can be made primarily on the basis of comparison of their n.m.r. spectra. The pertinent n.m.r. data are given i n Table II, with the pyrazoline drawn i n i t s preferred conformation. For the purpose of i l l u s t r a t i n g how n.m.r. was used to differentiate between two C-5 epimers, pyrazolines _30_ and _31 are chosen. Knowing the favoured conformation for _30 and 31, as drawn in Table II, i t i s expected that the acetyl methyl (7.61 T) of pyrazo-line 30' w i l l be at lower f i e l d than the acetyl methyl (7.77 x) of pyrazoline 31. However, the C-3 methyls w i l l be affected i n an opposite manner and the C-3 methyl (8.80 x) of ^ 0 w i l l be at higher f i e l d than the C-3 methyl (8.53 x) of 31. In a similar fashion, the relative positions of the other pertinent resonances (C-4 methyl, C-4 and C-5 hydrogens) can be nicely explained for pyrazolines 30^ and 31. - 40 -1 2 3 Table I I . N.m.r. data f o r t e t r a s u b s t i t u t e d p y r a z o l i n e s . ' Pyrazoline A c e t y l C-3 H-4 H-5 C-4 or C-5 methyl methyl methyl COCH, C^H 6 5 L N 7.61 8.82 8.1 5.37 8.96 // N 30 C 6 H 5 N 7.77 8.53 7.30 4.71 9.61 C0CH 3 / / N 31 N C H \ C 0 C H 3 M C 6 H 5 — J  // O N . COCH, i H5 \ / — N / / 7.98 8.42 8.. 5 5.16 9.02 7.57 8.70 7.7 4.70 9.80 7.61 9.01 6.85 5.31 8.53 34 - 41 -Table I I . (Continued) C 6 H 5 7.83 8.58 6.34 5.98 8.62 35 7.96 8.31 Chemical s h i f t s i n x u n i t s . Drawn i n preferred conformation. 3-Methyl-3-acetyl-l-pyrazollne-(103) i s also included f o r comparison. I t has been shown that both of i t s conformations are equally populated (4). - 42 -The chemical shift resonances of the next C-5 epimeric pair of pyrazolines, 32_ and 33, f a l l in line with the above rationalization. For the pyrazolines _34 and 35 - the acetyl methyl, the C-3 methyl, the C-5 methyl and C-4 hydrogen a l l have chemical shifts which are consistent with the explanation as explained above. However, the C-5 hydrogens of pyrazolines 3_4 and ' 35_ have the opposite relative chemical shifts from what is expected. It appears, that on comparison to other C-5 methyl pyrazolines, that the C-5 hydrogen of 34_ is much lower than expected. The low value of the chemical shift (5.31 T) suggests that the phenyl group is orientated in such a way as to deshield the cis C-5 hydrogen. This rationalization has been found to be consistent with nuclear Overhauser studies done on pyrazoline 35 (see Table n i and the following discussion). The main purpose for carrying out nuclear Overhauser experiments on pyrazoline _34_ was to confirm that the C-4 hydrogen and the C-5 methyl have a £is_-relationship. Irradiation of the C-5 methyl produced a significant enhancement of 27% in the integrated intensity of the C-4 hydrogen. Consequently, the C-5 methyl and the C-4 hydrogen must be in a close spatial orientation such that an effect of 27% can be observed. Such an orientation can only be realized in a cis arrangement to each other. H.G.S. molecular structure models were used to measure the o internuclear distances (A) (45b) between the C-5 methyl and the C-4 e o • hydrogen (2.8 A), and between the C-3 methyl and the C-4 hydrogen (4.0 A) - 43 -Table I I I . Observed Nuclear Overhauser Enhancements Compound Ir r a d i a t e d Hydrogens Observed Hydrogen Percent Enhancement N CH, / / H 34 C-4 phenyl C-5 H C-4 H C-3 COCH, C-5 CH 3 C-3 CH„ 13 11 0 0 -1 C-3 CH, C-5 H C-4 H 11 2 C-5 CH, C-5 H C-4 H 33 27 Measured as the increase i n the integrated area r e l a t i v e to the i n t e r n a l i n t e g r a l standard p-distance - see § 12 of the experimental. - 44 -of known trans-stereochemistry. A c i s distance of 2.8 A allows f o r 1 ° a maximum e f f e c t of 21% and the trans distance of 4.0 A allows f o r a maximum of le s s than 5% enhancement (45a). Accordingly, i r r a d i a t i o n of the C-3 methyl produced a 2% enhancement of the C-4 hydrogen. Cl e a r l y , t h e C-4 hydrogen and the C-5 methyl must possess a c i s r e l a t i o n s h i p . Another notable aspect of the nuclear Overhauser experiments i s that i r r a d i a t i o n of the C-3 methyl produced an 11% enhancement i n the C-5 hydrogen, a r e s u l t that i s consistent with the stru c t u r e assigned to pyrazoline 34. As was pointed out e a r l i e r , the r e l a t i v e chemical s h i f t p o s i t i o n s of the C-5 hydrogens of pyrazolines 214_ and 35^ were reversed. The r a t i o n a l i z a t i o n used to explain t h i s r e s u l t was based on the deshielding e f f e c t of the phenyl group on the C-5 hydrogen of 34. This reasoning 2 i s supported by nuclear Overhauser studies i n which the phenyl group was i r r a d i a t e d and an enhancement of 13% was noted i n the C-5 hydrogen. o An ortho hydrogen of the phenyl can approach as close as 1.5 A to the C-5 hydrogen of 34. For the favoured conformation of _3_5 t h i s distance o i s extended to 3.8 A. A rigourous analysis c o r r e l a t i n g distances and nuclear Overhauser enhancements i s undesirable f o r two reasons. The r e l a x a t i o n of the The maximum allowed e f f e c t cannot be observed experimentally since the C-4 hydrogen of 122 i s relaxed by at l e a s t three sources (1) C-5 methyl (2) C-3 methyl (3) C-3 phenyl. This does not, however, have any bearing on the assignment of stereochemistry about the C-4 C-5 bond of pyrazoline 122. Only the ortho hydrogens of the phenyl group w i l l contribute to the r e l a x a t i o n . The meta and para hydrogens can never approach close enough to make a s i g n i f i c a n t c o n t r i b u t i o n . - 45 -C-4 and C-5 hydrogens i s caused by several sources, and there i s the problem of conformational m o b i l i t y of the pyrazoline together with the lack of knowledge concerning accurate bond distances i n the pyrazoline skeleton. Chemical evidence supporting the assignment of stereochemistry to the C-5 isomeric pyrazolines i s supplied by the r e l a t i v e amounts of o l e f i n s formed thermally from each p a i r of epimers. The generally accepted mechanism f o r the formation of an o l e f i n from a 1-pyrazoline s u b s t i t u t e d at C-3 by an e l e c t r o n withdrawing group i s the concerted migration of hydrogen from C-4 to C-3 or C-5 with t r a n s o i d a l e l i m i n a t i o n of nitrogen (46), Figure 17. Such a mechanism can only operate i f the Figure 17. Concerted t r a n s o i d a l mechanism for the formation of o l e f i n s from pyrazolines bearing a C-3 e l e c t r o n withdrawing group. - 46 -migrating hydrogen occupies the pseudo-equatorial p o s i t i o n at C-4. Consideration of the t r a n s o i d a l e l i m i n a t i o n of nitrogen i n conjunction with the conformational preferences of the C-5 isomeric pyrazolines leads to the conclusion that the opportunity f o r hydrogen migration i s greater i n pyrazolines _3_1, J33_ and 35_ than i n t h e i r C-5 epimers 30, 32, and 3I4_ r e s p e c t i v e l y . This expectation i s r e a l i z e d as pyrazolines 30 and ^1 give 1 and 21% o l e f i n r e s p e c t i v e l y ; pyrazolines 32^  and 33 give 0 and 7% o l e f i n r e s p e c t i v e l y ; and pyrazolines 3>4_ and J35_ give 0 and 67% o l e f i n r e s p e c t i v e l y . Complete product d i s t r i b u t i o n s f o r each pyrazoline are l i s t e d i n Tables V I and V I I . Other chemical means used to d i f f e r e n t i a t e between p a i r s of C-3 isomeric pyrazolines depended upon the r e l a t i v e rates of thermal decomposition. Crawford et a l (6c) have shown that the r a t e of nitrogen expulsion from a pyrazoline molecule to form a cyclopropane i s decreased upon the occupation of the C-4 pseudo-axial p o s i t i o n of the pyrazoline, eqs. 50 and 51. This conclusion was reached by comparison of the r e l a t i v e rates of decomposition of 4-methyl-1-pyrazoline-(28) and 4,4-dimethyl-1-pyrazoline-(110). The mono substituted pyrazoline 28 decomposed 127 times f a s t e r than the d i s u b s t i t u t e d pyrazoline 110. An analogous s i t u a t i o n was thought to hold f o r the pyrazolines 30 to 35. That i s , the favoured conformation of pyrazolines .31, 33, and 35_ would have a substituent (methyl or phenyl) occupying the C-4 a x i a l p o s i t i o n more often than t h e i r respective C-5 epimers 30_, 32, and _3_4 (the pyrazolines 30 to 35_ are drawn i n t h e i r favoured conforma-t i o n i n Table I I ) . This leadsto the proposal that pyrazolines ^0_, 32, and j34_ w i l l decompose f a s t e r than t h e i r respective counterparts 3_1, 33 and 35. - 47 -Experimentally, i t was observed that pyrazoline _30 did indeed decompose about 9 times f a s t e r than 3^, and pyrazoline 32_ decomposed about 4 times f a s t e r than 33. However, the decomposition rates f o r pyrazolines 34_ and 35 were reversed from what was expected. In f a c t , pyrazoline '35_ decomposed greater than 10 times f a s t e r than 34. One pos s i b l e explanation might l i e i n the fac t that i n the case of pyrazolines studied by Crawford et a l (6c) the major decrease i n the rate of 4,4-dimethyl pyrazoline-(110) i s due to the entropy term, eqns. 50 and 51. I t would therefore appear that assignment of [50] cyclopropane o l e f i n 52.3 47.7 k = 1 015.85 e-42,200/RT [51] 98.6 1.4 i n14.10 -42,800/RT k = 10 e ' stereochemistry to isomeric pyrazolines such as 2h_ and 85 should be made on the basis of comparison of the a c t i v a t i o n parameters and not the o v e r a l l rates. In f a c t , i t may w e l l be that the entropy term for the cyclopropane forming re a c t i o n i s smaller f o r pyrazoline 35_ than f o r 34, but that the o v e r a l l increase i n the rate of _3_5_ over _34_ may w e l l be a r e f l e c t i o n of a much smaller a c t i v a t i o n energy f o r 35. - 48 -2. D i s t r i b u t i o n and I d e n t i f i c a t i o n of Products (a) Method of Decomposition The p y r o l y s i s of the pyrazolines was c a r r i e d out e i t h e r i n a sealed pyrex tube or i n the i n j e c t o r of the v.p.c. D e t a i l s are given i n the experimental. The d i r e c t photolysis of the pyrazolines were c a r r i e d out as d i l u t e s o l u t i o n s ranging from 4.0 to 18.8 mmolar i n d i e t h y l ether f o r o 0.5 to 2.75 h at 3500 A (Rayonet Reactor) using a pyrex r e a c t i o n v e s s e l . Table XXX Section 9(a) of the Experimental, gives d e t a i l s of i n d i v i d u a l experiments. For the s e n s i t i z e d photolyses, the pyrazolines 19, 20, 98, and 99 were photolyzed as 8.9 to 16.6 mmolar sol u t i o n s i n n-pentane f o r 0.7 o to 1.0 h at 3500 A (Rayonet Reactor) using a pyrex r e a c t i o n v e s s e l . Benzophenone i n a 10.4 to 25.6 molar excess was used as the s e n s i t i z e r . The re a c t i o n v e s s e l was purged with a stream of oxygen free nitrogen p r i o r to and during the r e a c t i o n period. The remaining pyrazolines 30 to J35_ were photolyzed as 4.1 to 6.9 molar so l u t i o n s f o r 0.5 to 1.0 h under s i m i l a r conditions as above. Table XXXI, Section 9(b) of the Experimental, gives d e t a i l s of i n d i v i d u a l experiments. (b) P h o t o l y t i c Control Experiments Owing to the fa c t that cyclopropyl ketones undergo a v a r i e t y of reactions upon d i r e c t or s e n s i t i z e d photolysis"'" over a range of For example, c i s - t r a n s isomerization (47-49), formation of ct,8-and 8,y-unsaturated ketones (51-53), y>6-unsaturated ketones (54), and dihydrofurans (38). - 49 -wavelengths, i t was necessary to subject the products of photolysis to s i m i l a r conditions used to photolyze the parent pyrazolines. o D i r e c t photolysis at 3500 A i n d i c a t e d that a l l the cyclopropyl ketones were photo stable at t h i s p a r t i c u l a r wavelength. Only the a, B-unsaturated ketones E_- and Z-100 were found to be photo l a b i l e i n that they undergo c i s - t r a n s isomerization. However, t h i s observation has no bearing onthe r e s u l t s . Experimental d e t a i l s are contained w i t h i n Table XXXII, Section 10 of the Experimental. o The s e n s i t i z e d p h o t o l y s i s c o n t r o l runs were c a r r i e d out at 3500 A with benzophenone as the s e n s i t i z e r . None of the cyclopropyl ketones underwent c i s - t r a n s isomerization, conversion to a dihydrofuran, or s t r u c t u r a l rearrangement to a,8 - and 8 ,y-unsaturated ketones, nor to Y,6-unsaturated ketones. However, i t would be expected that i f a s u i t a b l e s e n s i t i z e r were employed,that reactions of the nature described above would r e s u l t (see previous footnote). A c o n t r o l run was performed on a blank sample using only benzo-phenone and n-pentane. A f t e r p h o t o l y s i s and evaporation of the solvent, a n.m.r. spectrum was run on the residue. Several absorptions were noted i n the 8.2 to 9.4 T region with a s i n g l e t at 6.2 x. This s i n g l e t underwent deuterium exchange as evidenced by n.m.r. The residue observed i n the blank r e a c t i o n i s a r e s u l t of p i n a c o l formation and other r a d i c a l combinations (55). (c) Decomposition of the 3,4-Dimethyl Pyrazolines 98 and 99 Decomposition of pyrazolines *9_8 and 99_ gave f i v e i d e n t i f i a b l e products, eq. 52. Their product d i s t r i b u t i o n s are recorded i n Table IV. The s t a r t i n g m a t e r i a l 3-methyl-3-pentene-2-one a r i s i n g from d i r e c t photolysis was i d e n t i f i e d by i t s v.p.c. r e t e n t i o n time and i t s n.m.r. spectrum. No diazomethane was detected. The dihydrofuran 111 was i d e n t i f i e d by i . r . and n.m.r. The i . r . displayed a band at 1707 cm \ c h a r a c t e r i s t i c of the double bond of a dihydrofuran (4). The n.m.r. was consistent with the assigned stru c t u r e . I t contained two s i n g l e t s showing long range coupling at 8.32 and 8.44 T f o r the C-2 and C-3 methyls. A doublet was located at 8.98 T f o r the C-4 methyl, a m u l t i p l e t at 7.22 x f o r the C-4 hydrogen, and two m u l t i p l e t s resembling t r i p l e t s at 5.76 and 6.40 x f o r the C-5 hydrogens. A l l resonances have c h a r a c t e r i s t i c chemical s h i f t s when compared to s i m i l a r dihydrofuran d e r i v a t i v e s (4). The a,8-unsaturated ketone 112 was i d e n t i f i e d by n.m.r. I t s spectrum was i d e n t i c a l to that described by Cottee et a l (56). The 8,y-unsaturated ketone 113 was i d e n t i f i e d by i . r . and n.m.r. The i . r . Used to prepare the pyr a z o l i n e . - 5 1 -showed a carbonyl s t r e t c h i n g frequency at 1714 cm , a c h a r a c t e r i s t i c feature of 8 ,y-unsaturated ketones. The i . r . also showed a band at 1642 cm 1 for the carbon-carbon double bond. The n.m.r. was consistent with the proposed s t r u c t u r e . I t showed a s i n g l e t at 7.96 x f o r the a c e t y l methyl, a doublet at 8.88 T f o r the C-3 methyl, a s i n g l e t showing long range coupling at 8.34 T , a quartet at 6.83 x f o r the C-3 hydrogen, and a narrow m u l t i p l e t at 5.10 x f o r the C-5 v i n y l hydrogens. Table IV. D i s t r i b u t i o n of Products from Pyrazolines £8 and 99 Pyrazoline Conditions s .m. D.H.F. a , e - B,Y- cis - A trans - A I l l 112 113 114 115 Ac | H A-152° 0 6 62 6 16 10 A hv-d 1 13 t r . 0 0 86 1 \ N . 1 hv-s 0 4 0 0 91 5 cis-98 Ac • A-152° 0 18 18 4 27 33 V 1 hv-d 2 0 0 0 23 75 \ N hv-s 0 4 0 0 82 15 trans-99 hv-d,direct p h o t o l y s i s at 3500 A; hv-s, benzophenone s e n s i t i z e d p h o t o l y s i s . - 52 -The cyclopropyl ketones 114 and 115 were i d e n t i f i e d by comparison of v.p.c. r e t e n t i o n times, i . r . spectra, and n.m.r. spectra to authentic samples (4). Cd) Photolysis of 3,5-Dimethyl Pyrazolines 19 and 20 The p y r o l y s i s and d i r e c t photolysis of the pyrazolines 19_ and 20 have already been reported (4). The product d i s t r i b u t i o n s f o r these two processes are included i n Table V. [53] The s e n s i t i z e d photolysis y i e l d e d only two products, c i s - and , trans-1,2-dimethyi-l-acetyl cyclopropanes-(114) and (115) r e s p e c t i v e l y . Both were i d e n t i f i e d by comparison of t h e i r v.p.c. r e t e n t i o n times, i . r . spectra, and n.m.r. spectra to authentic samples (4). - 53 -Table V. D i s t r i b u t i o n 1 of Products f o r Pyrazolines 19_ and 20 Pyrazoline Conditions D.H.F. a, 8 a,8 B,y cis-A trans-A 117 E-118 Z-118 E-119 114 115 cis-19 trans-20 neat-100° 23 35 0 2 16 24 hv-d 2 6 1 0 6 59 28 . 2 hv-s 0 0 0 0 65 35 neat-100° 0 0 18 4 61 17 hv-d 2 2 1 4 21 70 hv-s 0 0 0 0 52 48 1 2 The thermal and d i r e c t p h o t o l y s i s r e s u l t s are from r e f . (4). hv-d, d i r e c t photolysis with a medium pressure Hg lamp; hv-s, benzo-phenone s e n s i t i z e d p h o t o l y s i s . (e) Photolysis of Tetrasubstituted 1-Pyrazolines The thermal r e s u l t s have been reported previously (15). The major products from the d i r e c t p h o t o l y s i s of the C-5 isomeric pyrazolines 30 to _35_ were the cyclopropyl ketones 35, 36, and _37 plus the s t a r t i n g materials phenyl diazomethane and 3-methyl-3-pentene-2-one. Only the cyclopropyl ketones 35, 36, and _37_ were observed from the s e n s i t i z e d p h o t o l y s i s experiments. (e) Photolysis of Tetrasubstituted 1-Pyrazolines The s t a r t i n g m a terial 3-methyl-3—pentene-2-one-(100) was i d e n t i f i e d by i t s v.p.c. r e t e n t i o n time and i t s n.m.r. spectrum. The other s t a r t i n g m a t e r i a l , phenyl diazomethane, was i d e n t i f i e d by i t s d i s t i n c t odour and the reddish colour of the ether s o l u t i o n a f t e r p h o t o l y s i s . The three cyclopropyl ketones _36_, 3_7, and _38_ were i d e n t i f i e d by t h e i r v.p.c. retention times and t h e i r n.m.r. spectra. Assignment of stereochemistry to the cyclopropanes 3b_ to ^ 38 i s discussed i n the next s e c t i o n of the Results. 1 Used to prepared the pyrazoline. - 55 -1 2 Table V I . D i s t r i b u t i o n ' of Products f or Pyrazolines 30 to 33 Pyrazoline Conditions S t a r t i n g M a t e r i a l Ac Ph O l e f i n Ph 36 Ph" 37 38 Ac 1 N thermal 0 A i hv-d 3 18 P h A — w 3 30 hv-s 0 1 0 2 98 82 98 0 0 0 1 0 0 Ph 32 thermal 0 12 22 41 25 hv-d 27 1 11 60 0 hv-s 0 6 90 3 0 thermal 0 91 6 3 0 hv-d 0 96 4 t r . 0 hv-s 0 94 5 1 0 thermal 0 26 22 45 7 hv-d 0 99 1 t r . 0 hv-e 0 99 1 t r . 0 Thermal r e s u l t s are taken from reference ( 1 5 ) . The photolysis r e s u l t s for 30_ and ^31 are those corrected to 100% using J30:_31 r a t i o s of 6 9 : 3 1 and 5 : 9 5 . The photolysis r e s u l t s f o r 32 and J33 are those corrected to 100% using 32_:3J3 r a t i o s of 4 : 1 and 2 : 3 . o hv-d,direct photolysis at 3500 A; hv-s, benzophenone s e n s i t i z e d photolysis, - 56 -[55] COCH i COCH h * i N / II or II A II \ 'I C 6 H 5 ^ « C 6 H 5 \ N 34 " 35 COCH, COCH3 C 6H 5 COCH3 C 6 H 5 E-125 Z-125 + / ^ O C „ 3 t C 6 H v ^ C O C H 3 + ^ COCH, 6 5 ^ C 6 H 5 Z-126 36 37 C 6 H 5 38 1 2 Table VII. D i s t r i b u t i o n ' of Products from Pyrazolines 34 and 35 Pyrazoline Conditions 36 P\A/C A/c O l e f i n 125 + 126 37 Ph 38 Ac • thermal 79 0 20 0 N hv-d 3 95 2 2 1 34 hv-s 3 96 2 2 t r . Ac thermal 21 5 6 67 A_I hv-d 26 0 47 25 35 hv-s 96 2 2 t r . Thermal r e s u l t s are from reference (15). 2 The photolysis r e s u l t s for J34_ and j35_ are those corrected to 100% using 34_:35 r a t i o s of 100:0 and 45:55. 3 0 hv-d, d i r e c t p h o t o l y s i s at 3500 A; hv-s,benzophenone s e n s i t i z e d p h o t o l y s i s . - 57 -3 c Stereochemical Assignment to the Cyclopropyl Ketones Correct assignment of stereochemistry i s particularly important in the decomposition of the tetrasubstituted pyrazolines, c i s - trans isomerization, 1 and conversion to dihydrofurans. 1 Thus, the assignments w i l l be b r i e f l y reviewed (15) together with additional data that contribute to the problem. Since the cyclopropane derivatives i n question are uniquely substituted at a l l three carbon centers, then i t i s necessary to establish the relative stereochemistry between two of the three bonds. Four independent pieces of evidence are presented, a l l of which suggest the same stereochemistry. There are four cyclopropane products possible (of which only three were isolated) from the decomposition of pyrazolines 3>0_ to 3 6 . The cyclopropanes are outlined i n Table VIII together with their n.m.r. 2 data. The stereochemistry between C-l and C - 3 was established on the principle that those cyclopropanes i n which the C-l acetyl and C - 3 methyl are in a cis orientation, w i l l rearrange to y»^-unsaturated ketones (57-59). The stereochemistry between C-2 and C - 3 was established on the observations of Patel et a l ( 6 0 ) that the c i s -vi c i n a l coupling constant ( 8 . 0 to 11.2 Hz) i s generally larger than the trans-vicinal coupling. 1 See the forthcoming sections dealing with the rearrangement of tetra-substituted cyclopropanes. 2 C-l bears a methyl and an acetyl C-2 bears a phenyl C - 3 bears a methyl. - 5 8 -Only one of' the cyclopropanes underwent rearrangement at 2 2 7 ° to the y>^-unsaturated ketones 1 2 3 and 1 2 4 , eq. 5 6 . This same cyclopropane had a H - 2 H - 3 v i c i n a l coupling constant of 6 . 4 Hz, indicative of a trans-relationship „ This establishes the structure of the cyclopropane as 3 6 . [ 5 6 ] H2C-H C 6H 5 3 6 CH, H CH30C- CH, H C 6 H 5 + H s2> -C 6 H 5 1 2 2 H COCH, r CH, H C 6 H 5 1 2 3 1 2 4 The remaining two cyclopropanes did not undergo rearrangement to the y,6-ketones 1 2 3 or 1 2 4 , this result placing the C-l acetyl and C - 3 methyl trans to each other. The H - 2 H - 3 v i c i n a l coupling of 7 . 0 Hz for one of the remaining cyclopropanes was indicative of a trans relationship and this cyclopropane was assigned the structure of 3 7 . The remaining cyclopropyl ketone with a H - 2 H - 3 cis coupling of 9 . 8 Hz was assigned the structure 3 8 . Other data are consistent with the assigned structures. Fi r s t of a l l , i n the case of 3 6 _ and 3 8 the acetyl methyls have normal resonances at 7 c 7 9 and 7 . 8 8 x respectively. On the other hand, 3 7 ^has an acetyl methyl resonance at higher f i e l d located at 8 . 3 2 x. In the former two - 59 -Table VIII. N.M.R. Data f o r Tetra s u b s t i t u t e d Cyclopropanes Cyclopropane Solvent A c e t y l C - l C-2 C-3 C-3 J _ _ CH 3 CH 3 H H CH 3 ' CC1. 4 7. .79 8. .92 7. .15 8. ,56 8. .85 6.4 COCH3 CDC1 3 7. .72 8. .89 7. .07 8. ,45 8. .83 C 6 H 6 8. .08 9. ,16 6. ,93 8. .81 8. .88 2 A -0. .14 0. ,36 0. .05 CCl. 4 8. .32 8. .54 8. .13 7. ,74 8. ,77 7.0 C 6 H 5 36 C H A COCH CDC1_ 8.18 8.49 7.98 7.65 8.76 : 6 H 5 v A ^ C O C H 3 C D C 1 3 C,H, 8.47 8.83 8.33 7.67 9.03 6 6 * A 0.35 0.02 0.27 A? C 6 H 5 38 CCl. 4 7.88 8.91 7.29 8.23 8.98 9.8 CDC1 3 7.75 8.85 7.17 8.13 8.94 C 6 H 6 8.13 9.07 7.17 8.25 9.18 2 A 0.00 0.12 0.24 3H 5 vAj°C H2 - not i s o l a t e d -39 1 N.m.r. chemical s h i f t s i n x u n i t s , coupling constants i n Hz. 2 A equals x - t (p.p.m.) 6 5 3 - 60 -cyclopropanes, the C-2 phenyl group i s trans to the a c e t y l function; whereas, i n the l a t t e r case of 37, the phenyl and a c e t y l substituents are c i s . This r e s u l t suggests that the phenyl i s s i g n i f i c a n t l y s h i e l d i n g the a c e t y l methyl when there e x i s t s a c i s relationship."'" A s i m i l a r s h i e l d i n g e f f e c t of the phenyl upon the C - l methyl i s also observed. Secondly, the n.m.r. solvent s h i f t study i s consistent with the assignment of stereochemistry to the cyclopropyl ketones. Of i n t e r e s t i s the magnitude and sign of the d i f f e r e n c e between the chemical s h i f t CDC 1 i n C,HC and CDC1„ (designated as 4 ^ i n p.p.m.) of a substituent D J J C,n c 6 3 v i c i n a l to the carbonyl function. In the case of the cyclopropyl ketones 36_, _3_7 and _38 the resonances of i n t e r e s t are therefore the C-2 hydrogen, the C-3 hydrogen, and the C—3 methyl. Several reports on cyclopropane d e r i v a t i v e s have appeared i n the l i t e r a t u r e (62a-f) dealing with the infl u e n c e of d i f f e r e n t solvents such as CCl^, CDCl^, C^H^ and C^H^N upon the p o s i t i o n of a chemical s h i f t resonance r e l a t i v e to the i n t e r n a l standard TMS. In one of CDC1 these reports, Boykin et a l (62c) found that the range of A 3 C 6 H 6 va r i e d from -0.17 to +0.07 p.p.m. for r i n g hydrogens c i s to the carbonyl group. On the other hand, a range of +0.17 to +0.43 p.p.m. was found for those r i n g hydrogens trans to the carbonyl function. CDC1 The values of A„ n 3 reported i n Table VIII f o r the r i n g hydrogens C 6 H 6 agree f a i r l y w e l l with the reported values (62c). CDC1 In another report, Strzalko and Seyden-Penne (62b) found A„ „ 3 _ C 6H 6 For a s i m i l a r e f f e c t on the methyl of a carbomethoxy function see reference (62). - 61 -values of +0.01 to +0.25 p.p.m. f o r methyl substituents c i s and trans to the a c e t y l moiety r e s p e c t i v e l y . Values of +0.05 for the methyl c i s to the a c e t y l i n cyclopropane 36_ and values of +0.27 and +0.24 p.p.m. for the methyls trans to the a c e t y l i n cyclopropanes 37_ and 38 r e s p e c t i v e l y agree w e l l with the reported values of Strzalko et a l 4. Rearrangement of Tetrasubstituted Cyclopropanes (a) General The cyclopropyl ketones J36_, 37_ and J38_ are uniquely s u b s t i t u t e d at a l l three carbons of the cyclopropane r i n g . For t h i s reason they were chosen as a basis f o r a stereochemical study of the conversion of a cyclopropyl ketone to a dihydrofuran, eq. 57. At the same time some information can be derived about the c i s - t r a n s isomerization r e a c t i o n . In add i t i o n , the cyclopropyl ketones are both thermally and photochemically l a b i l e and thus complementary r e s u l t s for both modes of reaction can be furnished. (62b). 36 [57] 96 97 38 COCH 3 - 62 -Table IX. N.M.R. Data f o r 4,5-Dihydrofurans Dihydrofuran C-4 methyl C-5 hydrogen J. H-4.H-5 w C 6 H 5 96 9.50 4.62 9.4 C 6 H 5 ° 97 8.88 5.16 8.0 C 6 H 5 ° 127 128 C 6 H 5 129 C 6 H 5 130 9.48 8.85 9.48 8.85 4.53 5.16 4.55 5.14 9.4 8.4 9.6 8.1 Chemical s h i f t s i n T u n i t s , coupling constants i n Hz. The n.m.r. data f o r 127 to 130 i s taken from reference (63). - 63 -There are two dihydrofuran stereoisomers p o s s i b l e from the thermal or photochemical rearrangement of the cyclopropyl ketones 36, 37, or J38, eq. 57. The pertinent n.m.r. data are l i s t e d i n Table IX which also includes two p a i r s of c l o s e l y r e l a t e d isomeric dihydrofurans 127 to 130 (63). The stereochemistry between C-4 and C-5 of the dihydrofuran was established f o r compounds 127 to 130 by n.m.r. on the assumption that the phenyl group w i l l s h i e l d the methyl that i s c i s at C-4 (63). This w i l l cause the C-4 methyl group c i s to the phenyl to appear at higher f i e l d thanthe C-4 methyl group orientated trans to the phenyl. On t h i s b a s i s , dihydrofuran 96_ with the C-4 methyl resonance at 9.50 was assigned the c i s stereochemistry. The other dihydrofuran 97_ with the C-4 methyl resonance to lower f i e l d at 8.88 was given the trans stereochemistry. Although v i c i n a l n.m.r. coupling constants have been used extensively to assign stereochemistry, the v i c i n a l H-4 H-5 couplings are of l i t t l e value i n the case of dihydrofurans. In the case of the dihydrof urans \96_, 97, and 127 to 130 the d i f f e r e n c e between c i s and trans couplings i s very small ranging from 1.0 to 1.7 Hz. Moreover, i t has been shown that f o r benzodihydrofurans the c i s couplings sometimes are la r g e r (64a) and at other times smaller (64b) than Ihe trans coupling. I t could be argued that the s h i e l d i n g e f f e c t of the phenyl r i n g on the adjacent C-4 methyl i s not a v a l i d approach. Thus nuclear Overhauser experiments''" were undertaken on the dihydrofuran 9_7 i n order See Table III for a record of r e s u l t s . - 64 -to confirm the trans-stereochemistry. I r r a d i a t i o n of the C-4 methyl produced a s i g n i f i c a n t i n t e g r a l i n t e n s i t y enhancement of 23% i n the C-5 hydrogen at 5.16 x. Accordingly, the C-4 methyl and the C-5 hydrogen must occupy a close s p a t i a l arrangement f o r such a large e f f e c t to occur. This s p a t i a l arrangement can only be i f the C-4 methyl and C-5 hydrogen are i n a c i s o r i e n t a t i o n . In support of the previous statement H.G.S. structure models were constructed of the dihydrofurans 96_ and 97. Distances between the C-4 methyl and C-5 hydrogen were measured (45b) and found to be 2.8 and o o 3.6-4.0 A for 96^  and _9_7 r e s p e c t i v e l y . The distance of 2.8 A allows 1 ° fo r a maximum enhancement of 21%; whereas,the 3.6-4.0 A distance allows for less than 6% enhancement (45a). I t i s c l e a r that the methyl and hydrogen have a c i s v i c i n a l r e l a t i o n s h i p . (b) Thermal and Photochemical Results Both the thermal and photochemical experiments were accomplished by using degassed samples of the cyclopropyl ketone i n sealed pyrex o tubing. The photochemical runs were done at 3100 A. The progress of the reac t i o n was monitored by a Perkin Elmer Model 226 a n a l y t i c v.p.c. The thermal r e s u l t s are recorded i n Tables X, XI and XII f o r the Exact maximum enhancements cannot be provided because of the lack of knowledge concerning bond distances i n the dihydrofuran skeleton, the conformation m o b i l i t y of the dihydrofuran molecule, and the rel a x a t i o n of the C-5 hydrogen by more than one source. - 65 -cyclopropyl ketones 36_, T7 and _38. The photochemical r e s u l t s are l i s t e d i n Tables XIII, XIV and XV r e s p e c t i v e l y . In the case of the cyclopropyl ketone _38, no information concerning the stereochemistry of dihydrofuran formation was attain a b l e i f the rea c t i o n was i n v e s t i g a t e d at a l a t e stage, mainly because of the competitive c i s - t r a n s isomerization of the cyclopropyl ketones _3_8 and 37. To circumvent t h i s problem the progress of the r e a c t i o n was monitored very c l o s e l y at an e a r l y stage before the competitive processes became too d i s t u r b i n g . Thus the r a t i o of the two dihydrofurans % . and 97_ was attained as early as 0.2 percent t o t a l formation of dihydrofuran product. The same approach was done f o r the cyclopropyl ketone 37, although i n t h i s case the competitive c i s - t r a n s isomerization did not i n t e r f e r e nearly to the extent as i n the case of 38. I t was not necessary to i n v e s t i g a t e the e a r l y course of the re a c t i o n i n the case of the cyclopropyl ketone 36_ as the r a t i o of the two dihydro-furans 96_ and 9J_ remained constant throughout. In the cases of the photochemical runs the progress of the r e a c t i o n i s not always dependent on time (see Tables XIII, XIV, and XV). The extent that the photochemical reactions proceeds i s also dependent on the power of the photochemical r e a c t i o n and on the p o s i t i o n of the rea c t i o n tube i n the reactor. Another aspect of the photochemical re a c t i o n i s the formation of a,8- and g,y-unsaturated ketones, 1 eq. 58. Their formation, however, does not have any bearing on the r a t i o of the dihydrof urans _96_ and 9_7 nor on the c i s - t r a n s isomerization r e a c t i o n . 1 This i s a well documented r e a c t i o n , see references (51-53). - 6 6 -Table X. Thermolysis of the Cyclopropyl Ketone 36." Temp., Time D.H.F. 96+97 123+124 A/c P\A/C A/c D-H-F-:^2,3 Ph 36_ 37 Ph 38 255.5 3.5 h 22 53 23 2 t r . 29:71 4.25 22 . 58 18 2 t r . 27:73 6.4 31 49 17 3 t r . 39:61 7.25 28 58 10 4 t r . 33:67 10.5 30 61 7 2 t r . 33:67 272.0 1.0 h 21 31 46 2 t r . 40:60 2.25 33 45 15 6 1 42:58 3.75 38 50 9 3 t r . 43:57 285.0 75 min 37 43 14 6 t r . 46:54 75 38 38 20 4 t r . 50:50 292.0 5 min 18 18 61 3 t r . 50:50 15 24 29 41 6 t r . 45:55 30 41 29 21 8 1 59:41 312.7 8 min 41 34 14 10 1 55:45 12 46 33 15 7 1 58:42 20 58 30 8 4 t r . 66:34 333.0 3 min 48 22 22 8 t r . 69:31 7 63 25 8 4 t r . 72:28 9 72 18 5 5 t r . 80:20 1 2 I n i t i a l concentration of 36_ > 99%. The r a t i o of D.H.F.:y6 changes i n favour of the dihydrofuran as the reaction progresses. The change i s not due to interconversion of the dihydrof urans with the ycS-unsaturated ketones. See the co n t r o l runs section 13(c). The r a t i o of the dihydrof urans 9jp_:97_ remains constant throughout at 3:97 re s p e c t i v e l y . - 67 -Table XI. Thermolysis of the Cyclopropyl Ketone J7 at 283.5°C Time D.H.F. yS i D.H.F. r a t i o 96+97 123+124 A Ac Ph A Ac A Ac Ph Ph 36 37 38 10 min 1.1 - 0.3 97.0 1.6 5:95 15 min 2.5 - 1.1 90.4 6.0 5:95 30 min 4.5 0.5 3.0 82.4 9.4 5:95 1.0 h 4.7 0.9 3.0 79.4 12.0 6:94 1.67 h 12.3 0.9 2.8 61.8 18.2 8:92 2.0 h 17.8 5.9 3.4 55.3 17.6 8:92 2.5 h 16.8 2.3 3.3 51.8 25.8 9:91 4.5 h 21.8 2.2 3.4 39.9 32.7 11:89 6.0 h 29.6 2.6 3.6 38.4 25.8 15:85 - 68 -Table XII. Thermolysis of the Cyclopropyl Ketone 38 at 283.5°C Time D.H.F. y& 96+97 123+124 Ph 36 D.H.F. r a t i o Ac 96:97 Ph 37 38 3 min 0.2 — 0.1 1.2 98.5 85:15 6 min 0.4 - 0.2 1.8 97.6 85:15 10 min 0.7 - 0.7 5.5 93.1 84:16 20 min 1.9 - 1.2 11.4 85.5 77:23 30 min 2.2 - 1.3 11.8 84.7 73:27 40 min 2.5 - 1.4 13.5 82.6 70:30 1 h 5.8 0.2 2.5 20.0 71.5 56:44 2 h 16.2 0.2 4.1 32.8 46.7 42:58 3 h 18.8 1.7 3.4 36.8 39.3 36:64 4 h 31.9 1.1 3.6 31.9 31.5 32:68 6 h 39.6 4.8 3.0 27.3 25.3 30:70 8.5 h 53.8 3.8 3.0 21.0 18.4 23:77 12.0 h 68.7 3.8 2.5 11.9 13.1 21:79 - 69 -o Table XIII. Photolysis of Cyclopropane 36 at 3100 A Time D.H.F. I * Ph A Ac A Ac Olefins 1 D.H.F. ratio (d) 96+97 / \ / c \A/ r\/ Ph' " • ^ 36 37 38 1 20 79 1 - t r . 3:97 2 48 49 3 - t r . 3:97 3 40 57 3 - t r . 3:97 4 52 45 3 - t r . 3:97 7 84 11 3 - t r . 3:97 8 85 10 3 - t r . 3:97 Includes a,g- and g,y-unsaturated ketones, see eq. 58. - 70 -o Table XIV. Photolysis of Cyclopropane 37 at 3100 A Time D.H.F. . O l e f i n s 1 D.H.F. r a t i o 9 6 + 9 7 1 Ac Ph A Ac A Ac 96=11 Ph* wc A ; 36 37 ? h 38 2 h 0.8 - 98 1 3:97 4 h 1.5 - 96 2 3:97 6 h 2.3 - 94 3 3:97 18 h 15 t r . 56 29 3:97 3 d 26 1 23 50 3:97 4 d 26 1 16 56 3:97 5 d 27 1 15 56 3:97 6 d 30 1 16 54 3:97 9 d 32 1 8 60 3:97 Includes a,8 - and 8 ,^-unsaturated ketones, see eq. 58. - 71 -o Table XV. Photolysis of Cyclopropane _38_ at 3100 A Time D.H.F. • O l e f i n s 1 D.H.F. r a t i o 16+97 A Ac Ph A Ac A Ac I^IZ NA/AC A / o Ph 37 38 2 h 0.2 — 2 96 1 83:17 3 h 0.6 - 3 95 1 85:15 4 h 1.4 - 8 88 2 74:26 6 h 1.6 - 9 86 3 69:31 18 h 5 1 20 64 10 52:48 3 d 18 1 19 16 46 34:66 4 d 24 1 15 14 47 28:72 5 d 22 2 14 11 53 25:75 6 d 26 2 14 8 51 26:74 9 d 32 2 9 1 56 18:82 1 Includes a,t 5- and 6 1 ^ - u nsaturated ketones, see eq. 58. - 72 -[58] Z-131 (c) Control Runs Known proportions of the dihydrof urans 96_ and 9_7 were both o thermolyzed at 284.2°C and photolyzed at 3100 A. The i n i t i a l r a t i o of 6^_:9_7 remained constant throughout and therefore do not i n t e r -convert under these conditions. Known r a t i o s of the dihydrof urans 96^  and 9_7 to the yfi-unsaturated ketones 123 and 124 were heated at 313.8° f o r a v a r i e t y of times. The r a t i o changed considerably i n favour of the dihydrofurans. This r e s u l t suggests that the yS-ketones disappear f a s t e r than the dihydro-furans, presumably by polymerization. - 73 -De t a i l s of the above c o n t r o l runs and others are found i n Section 13(d) of the Experimental. 5. K i n e t i c Studies (a) General The cyclopropyl ketones 132 and 135 were prepared by the a d d i t i o n 1 of phenyl diazomethane to methyl isopropenyl ketone, eq. 59 • Evaporation of the solvent followed by vacuum d i s t i l l a t i o n gave two products as in d i c a t e d by vapour phase chromatography. The two components were present i n a 2:1 r a t i o and were separated and c o l l e c t e d by v.p.c. The number of resonances, t h e i r m u l t i p l i c i t y and coupling constants were consistent with the gross s t r u c t u r e . COCH„ C.H,. A COCH„ A COCH3 I59J C 6H 5CHN 2 • = V 3 _ ^ 6 5 ^ 3 £ ^ CH-C 6 H 5 101 132 133 Assignment of stereochemistry to the isomeric c i s - t r a n s cyclopropyl ketones was made on two accounts. The f i r s t deals with the p o s i t i o n of the C - l and a c e t y l methyl resonances i n the n.m.r. In the case of the isomeric cyclopropyl ketones J36_, 31_ and (see Section 3, Table VIII) the observation was made that the a c e t y l methyls trans to the phenyl r i n g (ketones 36_ and 38) appeared at the normal p o s i t i o n of 7.72 and 7.88 x r e s p e c t i v e l y . On the other hand, the a c e t y l methyl of 37 (c i s to the phenyl) i s s h i f t e d u p f i e l d to 8.32 x. A 1 A- pyrazoline could not be i s o l a t e d i n t h i s case. - 74 -s i m i l a r s i t u a t i o n e x i s t s for the C - l methyls i n which the resonance are located at 8.92 and 8.91 x f o r J36 and _38 but the methyl of _37_ i s downfield at 8.54 x. The major cyclopropane from equation 59 has the a c e t y l methyl and C - l methyl at 8.33 and 8.54 x r e s p e c t i v e l y . The minor product has the a c e t y l and C - l methyl resonances at 7.87 and 8.98 x r e s p e c t i v e l y . Thus, the former i s assigned the c i s 1 structure 132; the l a t t e r , the trans stereochemistry of 133. Another piece of evidence that i s consistent with the assigned CDC1 stereochemistry i s the n.m.r. solvent s h i f t e f f e c t A„ „ 3 , see Table C 6 H 6 VIII of Section 3. In structure 133 the C-2 hydrogen which i s c i s to the a c e t y l function remains r e l a t i v e l y unchanged with the A value being 0.06 p.p.m. However, the C-2 hydrogen of 132 i s s h i f t e d u p f i e l d by 0.38 p.p.m. on going from CDCl^ to C^H^, r e s u l t s consistent with Boykin et a l (62c). The dihydrofuran 136 was prepared by thermolysis of the c y c l o -propyl ketones 132 and 133. The i . r . showed a band at 1701 cm 1 , a feature c h a r a c t e r i s t i c of dihydrofurans (4). The u.v. showed end absorption only. The m u l t i p l i c i t y of the resonances i n the n.m.r. spectrum were consistent with the assigned s t r u c t u r e . In ad d i t i o n , the peaks i n the n.m.r. had c h a r a c t e r i s t i c p o s i t i o n s (63) (see Table IX f o r s i m i l a r dihydrofuran d e r i v a t i v e s ) . The a,8- and 8,y-unsaturated ketones 134 and 135 r e s p e c t i v e l y were prepared by the thermolysis of the cyclopropyl ketones 132 and 1 Cis r e f e r s to the C - l a c e t y l and C-2 phenyl. - 75 -133, eq. 60. The a,8-unsaturated ketone 134 was i d e n t i f i e d by n.m.r. which had a s i n g l e t at 7.94 x for the a c e t y l methyl, a s i n g l e t showing long range coupling f o r the C-3 methyl, a doublet at 6.54 x for the C-5 hydrogens, and a t r i p l e t showing long range coupling at 3.34 x. No assignment of stereochemistry was made. [60] The g,y-unsaturated ketone was i d e n t i f i e d by n.m.r. There was a s i n g l e t f o r the a c e t y l methyl at 7.95 x, a doublet at 8.82 x f o r the C-3 methyl, a quintet at 6.79 x for the C-3 hydrogen, and a doublet of doublets at 3.89 x f o r the C-4 v i n y l hydrogen. In addition, there was a doublet at 3.53 x with a coupling constant of J = 16.0 Hz. On the basis of the large coupling constant the E_ stereochemistry was assigned to 135. (b) Experimental Conditions Preliminary studies ind i c a t e d that the progress of the rea c t i o n was extremely s e n s i t i v e to the proportion of the volume of the rea c t i o n - 76 -ve s s e l to the quantity of sample used. This proportion i s designated as V/S. When the proportion V/S was small the conversion of the cyclopropyl ketones 132 and 133 to the dihydrofuran 136 was f a s t e r than when the V/S proportion was large (see Table XVI). Moreover, when the V/S proportion was small, appreciable amounts of the q,g-134 and g,y-E-135 unsaturated ketones were formed, eq. 60. As the V/S proportion was increased the percentage of dihydrofuran 136 appeared to l e v e l o f f . In addition,the amount of o l e f i n s formed became n e g l i g i b l e . I t was therefore i n t h i s l e v e l l i n g o f f region that the k i n e t i c studies were performed on the conversion of the cyclopropyl ketones 132 and 133 to the dihydrofuran 136, eq. [61]. The rates and a c t i v a t i o n parameters are recorded i n Table XVII. [61] A 6 5 132 + 133 136 - 77 -Table XVI. Dependence of Volume to Sample Ratio.' v/s 2 D.H.F. Cyclopropanes O l e f i n s 136 132 + 133 134 + 135 30 54.9 34.6 10.5 39 55.2 33.0 11.8 64 55.0 33.8 11.2 89 53.3 38.6 8.1 118 51.6 45.1 3.3 147 46.1 53.9 -234 42.2 47.8 -236 44.0 55.6 -295 43.6 56.4 -309 42.6 57.6 -393 45.2 54.8 -Samples were degassed and heated at 284°C f o r 2 hours. 2 „ /„ . , .-. , volume of the reaction v e s s e l (ul) V/S i s defxned as : -z ; T— s i z e of sample ( y l ) Table 3 XVII. A c t i v a t i o n Parameters f o r Interconversion Cyclopropyl Ketone--Dihydrofuran Temp. (°C) k 1 + k 2 ( 1 0 5 s e c _ 1 ) k -k 1 AH^(kcal/mole) AS +(e.u.) 287.5 15.2 88.4:11.6 E 2 = 48.1 a log A 2= 14.9 279.6 8.10 88.8:11.2 270.0 3.84 89.1:10.9 A H270= 4 7 - ° AS+ 7 Q= +6.4 262.5 2.00 89.4:10.6 254.9 1.04 89.7:10.3 See eq. 62. E and log A cal c u l a t e d by l e a s t squares p l o t . 3. See Arrhenius p l o t i n Appendix I I I . - 78 -(c) C a l c u l a t i o n of Results Derivation of the rate constants are given i n Appendix I. The equations used to c a l c u l a t e the a c t i v a t i o n parameters are provided i n Appendix I I . [62] Cd) Attempted c i s - t r a n s Isomerization Studies of Cyclopropyl Ketones 132 and 133 An attempted study of the c i s - t r a n s isomerization of the c y c l o -propyl ketones 132 and 133, eq. 63, was desireable so that the a c t i v a t i o n parameters could be compared to those obtained f o r the C,H A COCH- A C0CH o [63J 6 \A/ — - A/ 3 C6»5 the conversion of 132 and 133 to the dihydrofuran 136 (see Table XVII). Unfortunately, the k i n e t i c r e s u l t s were not reproducible. For example, on heating samples of pure 132 for 12.0 hours at 225.0°C y i e l d s of the isomeric cyclopropane ranged from 47.6 to 65.1 percent. This r e s u l t represents about a d i f f e r e n c e of 100% i n the rates. Other runs were equally poor with the y i e l d of 133 ranging from 16.7 to 41.0%, and i n another case 46.8 to 57.5%. The reason f o r the lack of r e p r o d u c i b i l i t y i s not understood at t h i s time. A suggestion i s that the answer may l i e i n the manner i n Which the r e a c t i o n tubes are cleaned. A possible a l t e r n a t i v e to neat thermolysis i s the use of a solvent such as benzene or cyclohexene. Although no values f o r the a c t i v a t i o n parameters were obtained for the c i s - t r a n s isomerization process, one u s e f u l r e s u l t i s that c i s - t r a n s isomerization occurs much f a s t e r than the conversion of the cyclopropanes 132 and 133 to the dihydrofuran 136. A u s e f u l range to study c i s - t r a n s isomerization i s estimated to be about 200 to 235°C; whereas, the range used to study the cyclopropyl ketone to dihydrofuran r e a c t i o n extended from 255 to 290°C. I t i s estimated that the d i f f e r e n c e i n the rates of the two processes i s between one to two powers of ten, the c i s - t r a n s isomerization being the f a s t e r . - 80 -I I I . MECHANISTIC DISCUSSION 1. Pyrazoline Decomposition (a) General The thermal decomposition of 1-pyrazolines has gained considerable a t t e n t i o n since 1961 when s i g n i f i c a n t contributions to the problem began to appear i n the l i t e r a t u r e . In most cases, the findings of the d i r e c t photolysis r e s u l t s have been published e i t h e r j o i n t l y with the thermal r e s u l t s or i n a separate p u b l i c a t i o n . The s e n s i t i z e d photolysis of 1-pyrazolines has gained somewhat les s a t t r a c t i o n , perhaps because of the seemingly le s s complexity of the problem. As a matter of course, the best p r a c t i c e i s to describe each of the three important processes together, that i s , the thermal decomposition, the d i r e c t photolysis and the s e n s i t i z e d p h o t o l y s i s . Thus f a r , a l l the stereochemical work r e l a t e d to d i r e c t and s e n s i t i z e d p h o t o l y s i s of 1-pyrazolines has been confined to e i t h e r c i s - and trans-3,4-d i s u b s t i t u t e d or to c i s - and trans-3,5-disubstituted-1-pyrazolines whose product d i s t r i b u t i o n s are r e s t r i c t e d to only two isomeric cyclopropanes. Further r e s u l t s of this nature are presented i n t h i s work, and i n a d d i t i o n , the formation of cyclopropanes from 1-pyrazolines i s i n v e s t i -gated by using pyrazolines that are uniquely substituted at a l l three ri n g carbons. These pyrazolines now have the advantage that they can p o t e n t i a l l y decompose to four isomeric cyclopropanes, thus information - 81 -can be derived about the degree of retention or i n v e r s i o n at carbons -3 and -5 of the s t a r t i n g pyrazoline. The fate of C-3 and C-5 w i l l be designated as follows. For example, ( r , i ) w i l l i n d i c a t e r e t e n t i o n at C-3 and i n v e r s i o n at C-5. The remaining three designations are ( r , r ) , retention at both centers; ( i , r ) i n v e r s i o n at C-3 only; and ( i , i ) , double i n v e r s i o n . Figure 18 i l l u s t r a t e s the four p o s s i b l e r e s u l t s i n cyclopropane formation. (r , r ) ( r , i ) ( i , r ) ( i , i ) Figure 18. Decomposition routes a v a i l a b l e for t e t r a s u b s t i t u t e d - 1 -pyrazolines. The 1-pyrazolines prepared i n this work have been l i s t e d i n Table I of the Results, p. 32. The pyrazolines consist of a s e r i e s of 3-methyl-3-acetyl d e r i v a t i v e s of 1-pyrazoline and the d i s c u s s i o n surrounding the 1-pyrazolines w i l l be divided i n t o two p a r t s . F i r s t l y , the isomeric c i s - and trans-3,A- and 3,5-pyrazolines w i l l be considered, and i n the second part, the decomposition of the t e t r a s u b s t i t u t e d 1-pyrazolines w i l l be examined. - 82 -(b) C i s - and Trans-3,4- and 3,5-Disubstituted-l-Pyrazolines ( i ) Non-Cyclopropane Forming Reactions The photolysis r e s u l t s i n Tables IV, p. 51 and V, p. 53 of the Results bring to focus several important aspects other than those dealing with cyclopropane formation that should be dealt with f i r s t . One such aspect i s that the degree of formation of a,8- and 8,y-unsaturated ketones i s s u b s t a n t i a l l y decreased on going from the thermal mode of decomposition to the d i r e c t photolysis route. This r e s u l t i s t y p i c a l of 3-acetyl (4) and 3-carbomethoxy-1-pyrazolines ( l a , b ) . On the other hand, pyrazolines s u b s t i t u t e d only with a l k y l groups (8b) can show l i t t l e change and at times a s u b s t a n t i a l increase i n the amount of o l e f i n formed on going from thermolysis to d i r e c t p h o t o l y s i s . On going to the s e n s i t i z e d p h o t o l y s i s of pyrazolines however, the observation i s that the o l e f i n formation i s n e g l i g i b l e . This r e s u l t i s e n t i r e l y consistent with the r e s u l t s found f o r other pyrazolines studied (8b,20,65,66). In some instances, i t has been observed that a small amount of o l e f i n i s sometimes formed but t h i s may be due to some decomposition by d i r e c t p h o t o l y s i s . A second observation concerns the reverse c y c l o a d d i t i o n cleavage r e a c t i o n . As revealed i n Table IV, p. 51, the pyrazolines cis-98 and trans-99 form the s t a r t i n g o l e f i n 3-methyl-3-pentene-2-one on d i r e c t p h o t o l y s i s , eq. 64. - 83 -[64] N N trans-99 Two routes f o r the formation of cleavage products have been proposed (8b), one v i a the formation of a trimethylene intermediate (Figure 19, route I ) , and the other producing a diazo compound plus the o l e f i n d i r e c t l y (Figure 19, route I I ) . Both eventually lead to the production of methylene and N„. Figure 19. Mechanism of reverse c y c l o a d d i t i o n r e a c t i o n for pyrazoline decomposition. - 84 -The decomposition of the pyrazoline 9J3 or 99_ does not help i n choosing between the two mechanisms; however, the decomposition of the t e t r a s u b s t i t u t e d pyrazolines 30_ and J3JL to be discussed i n the next section does permit a choice to be made, see p. 91. The l a s t observation to be commented on before dealing with the production of cyclopropanes i s the dihydrofuran forming r e a c t i o n . Generally, the dihydrofuran i s formed i n l a r g e s t amounts by the thermal decomposition of the 3-acetyl s u b s t i t u t e d pyrazoline. The p h o t o l y s i s , e i t h e r d i r e c t or s e n s i t i z e d , does not appear to be a very important pathway. It has been shown (4) that s t e r i c f a c t o rs i n the s t a r t i n g pyrazoline influence the amount of dihydrofuran formed thermally. In the case of pyrazolines 19_ and 20_ the dihydrofuran 117 i s formed i n 23 and 0% r e s p e c t i v e l y . This r e s u l t was explained by assuming a d i p o l a r Figure 20. Formation of a dihydrofuran from pyrazolines T9_ and 20. - 85 -intermediate with negative charge built up at C-3 of the pyrazoline. As this negative charge i s delocalized into the carbonyl oxygen, the oxygen w i l l be able to participate i n a ring closure reaction. The dihydrofuran formation should therefore be more favourable i f the oxygen is i n a position close to C-5 of the pyrazoline. Such is the case for the pyrazoline 19 but not for pyrazoline 20, Figure 20. ( i i ) Cyclopropane Forming Reaction Table XVIII. Cyclopropane Distributions for the Cis- and Trans-3,4-and 3,5-Pyrazolines. Pyrazoline Conditions Af vA/c Geometrical Retention cis-114 trans-115 Ac N N cis-98 A hv-d hv-s 10 86 91 10 1 5 50 99 95 A hv-d hv-s 27 23 82 33 75 15 55 77 15 j | 'Ac hv-d N = N cis-19 hv-s 16 59 65 24 28 35 40 68 65 - 86 -Ac 61 22 A 17 21 70 77 N = N trans-20 hv-s 52 48 48 1 Cyclopropane with the same geometrical r e l a t i o n s h i p f o r the substituents as the s t a r t i n g p y r a z o l i n e / t o t a l cyclopropane X 100%. 2 Taken from r e f . (4). Table XVIII i l l u s t r a t e s two important features of the p h o t o l y s i s r e a c t i o n . The f i r s t i s that the d i r e c t photolysis proceeds with a greater degree of geometrical retention than does the s e n s i t i z e d p h o t o l y s i s . The d i r e c t photolysis can be thought of as a pyrazoline molecule which undergoes simultaneous cleavage of the two C-N bonds to produce a 1,3-diradical that eventually couples to give a c y c l o -propane product. The l e s s e r degree of geometrical r e t e n t i o n associated with the s e n s i t i z e d r e a c t i o n i s i n l i n e with a t r i p l e t d i r a d i c a l intermediate whose l i f e t i m e i s longer owing to the necessity of s p i n i n v e r s i o n to a s i n g l e t before r i n g closure can take place. The d i r e c t p h o t o l y s i s , on the other hand, produces an excited s i n g l e t which can couple d i r e c t l y and thus a greater degree of geometrical retention i s expected. S t e r e o s p e c i f i c i t y would be expected i f the d i r e c t photolysis proceeded by a symmetry allowed reverse 2+2 c y c l o -a d d i t i o n r e a c t i o n . However, such reactions appear to be the exception rather than the r u l e (lb,20). That the d i r e c t photolysis of a pyrazoline proceeds with a greater degree of geometrical retention than the corresponding s e n s i t i z e d photolysis i s not always true as has been shown, for example, i n the - 87 -case of c i s - and trans-3,5-dimethyl-l-pyrazolines 21 and 22 r e s p e c t i v e l y (8b) (see Table XIX). This suggests that f o r some pyrazolines another mechanism i s working, one p o s s i b i l i t y being that the d i r a d i c a l produced i s a T r-cyclopropane intermediate that has a strong tendency to undergo conrotation, although not as strong a tendency as i n the thermal decomposition (8b). Table XIX. Cyclopropane D i s t r i b u t i o n s f o r Other Cis-Trans-3,4-and 3,5-Pyrazolines. Pyrazoline Conditions c i s or endo trans or exo % Geomet- Ref. cyclopropane cyclopropane r i c a l x Retention C0 2CH 3 hv-d hv-s C0 2CH 3 N = N trans-72 hv-d hv-s 100 95 0 86 0 5 100 14 100 95 100 14 20 20 N = N cis-69 hv-d-gas hv-d-EtOH hv-s 43.0 60.4 32.1 37.6 26.4 66.2 53 70 33 8b N N trans-70 hv-d-gas hv-d-EtOH hv-s 24.4 13.0 22.4 37.2 50.7 72.4 59 80 76 8b - 88 -N==N cis-21 hv-d-gas hv-d-EtOH hv-s 47.1 33.9 38.9 42.5 61.7 60.1 53 35 39 8b N N trans-22 hv-d-gas hv-d-EtOH hv-s 59.5 44.5 38.8 26.7 45.6 61.2 31 51 61 8b N N endo-137 N N exo-138 ( C H 2 ) 4 N==N cis-139 ( C H 2 ) 4 N N trans-140 hv-d hv-s hv-d hv-s hv-d hv-s hv-d hv-s 61.0 40.6 21.3 31.1 100 93 4 50 29.8 59.4 62.2 68.9 0 7 96 50 67 41 75 69 100 93 96 50 65 65 66 66 See footnote 1, Table XVIII. - 89 -The second important feature concerning the s e n s i t i z e d r e a c t i o n that Table XVIII brings to our a t t e n t i o n i s the r a t i o of the c i s - and trans-cyclopropanes. For the case of pyrazolines cis-98 and trans-99,the c i s : t r a n s cyclopropane r a t i o i s 91:5 and 82:15 r e s p e c t i v e l y . This r e s u l t i n d i c a t e s that the t r i p l e t d i r a d i c a l generated i s not capable of reaching conformational e q u i l i b r i u m before r i n g closure occurs. I f the r o t a t i o n rate i n the d i r a d i c a l were many times greater than the c y c l i z a t i o n rate, then the r a t i o of cyclopropanes would be expected to be i d e n t i c a l from both pyrazolines 98 and 99. A s i m i l a r s i t u a t i o n e x i s t s f or pyrazolines cis-19 and trans-20 i n that the former gives a c i s : t r a n s r a t i o of cyclopropanes of 55:35 r e s p e c t i v e l y ; whereas, the l a t t e r gives a r a t i o of 52:48 re s p e c t i v e l y . This r e s u l t i s i n l i n e with other 3,4- and 3,5-cis- and t r a n s - l - p y r a z o l i n e s , see Table XIX. The degree that the d i r a d i c a l can proceed to conformational e q u i l i b r i u m v a r i e s somewhat. In the case of cis-21 and trans-22, almost i d e n t i c a l cyclopropane r a t i o s are reached from both pyrazolines. On the other hand, the cyclopropane r a t i o s from other pa i r s of pyrazolines are not i d e n t i c a l , the l a r g e s t d i f f e r e n c e being found for the pyrazolines cis-139 and trans-140. A notable aspect of the above r e s u l t s i s that the c i s : t r a n s r a t i o of the cyclopropanes 114 and 115 from the 3,4-dimethyl-3-acetyl-l-pyrazolines 9<8 and £9 v a r i e s from 91:5 to .82:15; however, the c i s : trans cyclopropane r a t i o from the isomeric 3,5-dimethyl-3-acetyl pyrazolines 19 and 20_ i s i n the somewhat d i f f e r e n t range of 65:35 to 52:48 (see Table XVIII, p. 59 ). Although we might a n t i c i p a t e that the - 90 -d i r a d i c a l would be influenced on r i n g closure by the same s t e r i c factors that determine the equ i l i b r i u m p o s i t i o n 1 of the cyclopropanes, t h i s does not appear to be the case since the product r a t i o s do vary from 91:5 to 82:15 for pyrazolines 98 and 99_ and from 65:35 to 52:48 fo r the isomeric pyrazolines 19_ and 20. These values are c l e a r l y not asymptotic to a s i n g l e equilibrium value. In an analogous study, Crawford et al.(8b) found that the d i r a d i c a l from the cis-69 and trans-70 3,4-dimethyl-1-pyrazolines and the d i r a d i c a l from the cis-21 and trans-22-3,5-dimethyl-l-pyrazolines (see Table XIX) did not close to 2 an e q u i l i b r i u m mixture of the dimethylcyclopropanes but to a r a t i o which r e f l e c t s the various t r a n s i t i o n state energies of the d i r a d i c a l s f o r the r i n g closure r e a c t i o n . (c) T e t r a s u b s t i t u t e d - l - P y r a z o l i n e s (i ) Non-Cyclopropane Forming Reactions Three points were mentioned under t h i s heading i n the decomposition of 3,4- and 3,5-dimethyl-3-acetyl-pyrazolines: o l e f i n formation, formation of s t a r t i n g materials, and dihydrofuran formation. The data contained i n Table VI, p. 55 and VII, p. 56 of the Results f o r the te t r a s u b s t i t u t e d 1-pyrazolines are s i m i l a r i n many respects. In the case of the t e t r a s u b s t i t u t e d 1-pyrazolines, the degree of formation of a,8- and 8,y-unsaturated ketones i s lessened on going from 1 The equilibrium p o s i t i o n of the cyclopropanes 114 and 115 has not been determined. 2 The equilibrium p o s i t i o n of cis-26 and trans-25 dimethyl cyclopropane i s 28.4:71.6 r e s p e c t i v e l y at 380.0°C (29a). - 91 -thermal conditions to the d i r e c t photolysis mode. Again,as for other pyrazolines (8b,20,65,66), the s e n s i t i z e d photolysis y i e l d s a n e g l i g i b l e amount of o l e f i n . The reverse c y c l o a d d i t i o n r e a c t i o n i s also observed. In these cases, however, a d d i t i o n a l information i s derived about the mechanism. Two routes were considered (see Figure 19, p. 83 ), the second one producing a diazo compound. When both pyrazolines ^0 and J l were o subjected to direct photolysis at 3500 A, the r e s u l t i n g s o l u t i o n became red i n colour i n d i c a t i n g the presence of phenyl diazomethane. For th i s reason, route II (Figure 19, p. 83 ) i n which the diazo compound i s formed i n t a c t i s favoured. Prolonged photolysis would then lead to the appropriate carbene plus nitrogen by photodecomposition of the diazo compound. The t h i r d byproduct re a c t i o n expected i s dihydrofuran formation. Dihydrofurans have been observed as the r e s u l t of thermal decomposition of pyrazolines (A), or from the thermal (37a,b,c) and photochemical (38) rearrangement of cyclopropyl ketones. I t i s i n t e r e s t i n g , therefore, that dihydrofuran formation does not occur i n any mode of decomposition from the t e t r a s u b s t i t u t e d pyrazolines. This i s a curious feature since i t might be expected that r i n g closure from the carbonyl oxygen to the C-5 carbon would be e s p e c i a l l y f a c i l e i n pyrazolines _31_, _32_ and 35 since the a c e t y l group i s i n a favourable p o s i t i o n to form a C-5 to oxygen bond 1 (A) (see Figure 20, p. 8A). See Table I I , p. AO of the Results where the t e t r a s u b s t i t u t e d pyrazolines are drawn i n t h e i r preferred conformation. - 92 -( i i ) Cyclopropane Forming Reaction The t e t r a s u b s t i t u t e d 1-pyrazolines o f f e r the opportunity f o r us to d i f f e r e n t i a t e between the four possible stereochemical r e s u l t s i n the decomposition to cyclopropanes, that i s , ( r , r ) , ( r , i ) , ( i , r ) , and ( i , i ) (see Figure 18, p. 81 f o r an explanation of the no t a t i o n ) . We can make the following general comments f o r the d i r e c t and s e n s i t i z e d p h o t o l y s i s . The d i r e c t p h o t o l y s i s of the pyrazolines ^ 30 to _3_5_ give cyclopropanes having to a greater degree the same geometrical r e l a t i o n of the substituent groups as the pyrazolines than does the s e n s i t i z e d p h o t o l y s i s . However, this s t e r e o s e l e c t i v i t y i s not great enough to overcome the resistance to form cyclopropane 39_ as pyrazoline _3_3 gives none of 39. When (r,r ) would be predicted to give _39_ from pyrazoline 33^, the major pathway adopted leads to ( r , i ) . Also when ( r , r ) would be predicted to give cyclopropane 38 from pyrazolines 31 and 35, 38 i s the major product but considerable 37_ i s formed by the ( r , i ) process. Table XX. D i s t r i b u t i o n of Cyclopropanes from Tetrasubstituted 1-Pyrazolines. Pyrazoline Condi- I I % Geomet-tions A A C P h A A c A A c P h A A c r i c a l 1 Z V V/V l h / V/V Retention * $ % P h 36 37 P h 38 39 r , r r , i i , i 98 0 0 99 82 0 0 100 98 0 0 98 - 93 A hv-d hv-s 1 , 1 13 1 6 r , i 25 11 90 41 60 3 0 0 0 52 83 3 A hv-d hv-s r , r 91 96 94 i , r 6 4 5 l , i 3 0 1 r , i 0 0 0 91 96 94 r , i 26 99 99 1 , 1 22 1 1 i , r 45 0 0 r , r 0 0 0 0 0 0 r , r 79 95 96 i , r 0 2 2 r , i 20 2 2 1 , 1 0 0 0 89 96 96 r , i 21 26 96 i , i 5 0 2 r , r 6 47 2 i , r 0 0 0 19 64 2 Cyclopropane with the same geometrical r e l a t i o n s h i p f or the substituents of the s t a r t i n g p y r a z o l i n e / t o t a l cyclopropane X 100%. A: neat thermolysis, r e f . (15) - 94 -3 ° hv-d: d i r e c t photolysis at 3500 A. hv-s: benzophenone as s e n s i t i z e r . ^ The stereochemical fate of C-3 and C-5 i s denoted by the symbols r (retention) and i ( i n v e r s i o n ) , see Figure 18. The r e s u l t s from the s e n s i t i z e d r e a c t i o n given i n Table XX give more d e f i n i t i v e information. The s e n s i t i z e d decomposition, as has already been s t r e s s e d , i s expected to produce a t r i p l e t d i r a d i c a l whose l i f e t i m e should be longer than the corresponding s i n g l e t d i r a d i c a l . This longer l i f e t i m e of the t r i p l e t allows f o r more r o t a t i o n s and the p o s s i b i l i t y of reaching conformational e q u i l i b r i u m f o r the d i r a d i c a l before r i n g closure occurs. The product d i s t r i b u t i o n s can then r e f l e c t the b a r r i e r to r i n g closure which should r e l a t e to the r e l a t i v e s t a b i l i t y of the four p o s s i b l e cyclopropanes. I t i s c l e a r from Table XX, however, that r i n g closure i s competitive with r o t a t i o n i n the intermediate d i r a d i c a l . This point i s most strongly exemplified by observing the product d i s t r i b u t i o n s from pyrazolines 30 and 32. E q u i l i b r a t i o n of the d i r a d i c a l by free r o t a t i o n of the C-3 C-4 bond ( i , r ) would give the same conformation of the intermediate d i r a d i c a l from 30_ and 32_, however, pyrazoline 30_ gives 98% 37_ and pyrazoline 32^  gives 94% 36. Pyrazolines _30 and _31, on the otherhand, can give the same conformation of the d i r a d i c a l by a r o t a t i o n of the C-4 C-5 bond ( r , i ) and f o r the s e n s i t i z e d r e a c t i o n t h i s s i t u a t i o n occurs as 30_ and _31_ give 31_ as the major cyclopropane i n 98% and 90% r e s p e c t i v e l y . Likewise, pyrazolines 32^  and 33^ give the cyclopropane 36 i n 94% and 99%, r e s p e c t i v e l y . A t h i r d p a i r of p y r a z o l i n e s , 34_ and 5^_ which are also C-5 epimers, decompose to y i e l d cyclopropane _36 i n - 95 -96Z each. It is this variety of free rotation in the intermediate 1,3-diradical which i s one of the useful features in the decomposition of the tetrasubstituted 1-pyrazolines. This feature allows some information to be derived on how the diradicals behave as they proceed towards cyclopropane products. At this juncture i t i s worthwhile to point out the common feature for the group of pyrazolines 0^_, 32_ and 3_4_, and the common feature of the second group of pyrazolines 31, 33, and 35. In the former group, the exceptionally high degree of geometrical retention i s related to the formation of either cyclopropane 3_6_ or _3_7, by the double retention process ( r , r ) . The feature common to the latter group i s that the geometrical retention (r,r) cyclopropane product would result i n one of the less favourable cyclopropanes or 39_ (with 3 substituents c i s ) ; however, the main cyclopropane products from pyrazoline 31, 33, and 35 are once again 36 or 3]_ (96, 100 and 98% respectively) by an (r,i) process. This implies a particularly large barrier to closure to a cyclopropane with 3 groups c i s , such that a C-4 C-5 bond rotation can compete with closure. As i s the case for a single rotation about the C-3 C-4 bond ( i , r ) , a double inversion ( i , i ) appears to be only a minor pathway. That the ( i , i ) process i s minor i s il l u s t r a t e d by observing the ratio of cyclopropanes J36_ and 37_ from the group of pyrazolines 31, 33, and 35. Decomposition of J3JL, for example, prefers to give 37_ (r,i) rather than 3S_ ( i , i ) . On the other hand, pyrazolines 33 and 35 prefer to give 36 (r,i) rather than _37_ ( i , i ) . Only the thermal reaction appears capable of giving ( i , i ) or (i,r) products in appreciable amounts. - 96 -Having described the general behaviour of the trimethylene d i r a d i c a l produced from the s e n s i t i z e d photolysis of the t e t r a s u b s t i t u e d 1-pyrazolines, i t may seem f i t t i n g at t h i s point to speculate on the s t r u c t u r a l nature of t h i s d i r a d i c a l . However, disc u s s i o n regarding t h i s point w i l l be deferred to a l a t e r point a f t e r the stereochemical r e s u l t s concerning the thermal and photochemical rearrangement of the cyclopropyl ketones has been commented on, see p. 105. 2. Cyclopropyl Ketone-Dihydrofuran Rearrangement (a) General The nature of the mechanism of the conversion of a cyclopropyl ketone to a dihydrofuran has yet to be i n v e s t i g a t e d although the reaction has been reported to proceed both thermally (37a,b,c) and photochemically (38). Formally, t h i s conversion i s s i m i l a r to the formation of a cyclopentene from a vinylcyclopropane, a reaction which has gained wide a t t e n t i o n (30-33). The dihydrofuran problem i s of i n t e r e s t because of i t s connection to the v i n y l cyclopropane-cyclopentene system and because of the recent upsurge of i n t e r e s t i n symmetry allowed thermal rearrangements, p a r t i c u l a r l y sigmatropic s h i f t s . In t h i s f i r s t attempt to study the mechanism of the cyclopropyl ketone-dihydrofuran conversion, stereochemistry and k i n e t i c s are the main probes. The cyclopropyl ketones are uniquely substituted at a l l three r i n g carbons and thus can give some information about the stereochemical pathway. Moreover, the reaction proceeds both thermally and photochemically and therefore complementary r e s u l t s can be obtained f o r the two modes of r e a c t i o n . - 97 -Table XXI. Results for Cyclopropyl Ketone-Dihydrofuran Conversion. Cyclopropane Conditions Ratio Geometrical 1 V / ^ / Retention x y - x Y Ph 0 Ph 0 cis-96 trans-97 1 A; COCH3 285.0° 3:97 97% Ph hv-d 3:97 97% 36 Ph A C0CH„ 285.0° 5:95 95% 3 37 hv-d 3:97 97% A/ C0CH 3 285.0° 85:15 85% Ph hv-d 83:17 83% 38 The dihydrofuran with the same geometrical r e l a t i o n s h i p f o r the phenyl and methyl substituents of the s t a r t i n g cyclopropane/total dihydrofuran X 100%. This reaction i s a [1,3] sigmatropic rearrangement of a carbon migrating from a carbon to an oxygen. The r e s u l t s presented i n Table XXI contain two important features. The f i r s t i s the high degree of s t e r e o s e l e c t i v i t y with r e t e n t i o n i n the migrating group. In the case of the cyclopropyl ketones 36^ and 37_ with the C-2 phenyl and C-3 methyl - 98 -i n a trans o r i e n t a t i o n , the retention of geometry ranges from 95 to 97%. In the case of the cyclopropyl ketone _38, with the phenyl and C-3 methyl d s , the geometrical retention i s reduced to 83-85%. A second important feature involves the s i m i l a r i t y of the stereochemistry of the rearrangement whether the rea c t i o n proceeds thermally or photochemically. In l i g h t of these two observations, the mechanistic pathway can now be discussed f o r the conversion of thecyclopropyl ketones 36, 37 and _38_ to the dihydrof urans _96_ and 97_. Two choices are a v a i l a b l e , that i s , a concerted r e a c t i o n versus a step-wise process. Much the same s i t u a t i o n holds f o r the vinylcyclopropane-cyclopentene r e a c t i o n and many studies have been performed on t h i s system but as yet no unanimous agreement has been reached regarding the mechanism. On one hand, a d i r a d i c a l intermediate i s favoured (25a,30a,b,32a,b), and on the other side, a concerted mechanism i s considered correct (31,33a,b,c). (b) The Concerted Mechanism The conversion of a cyclopropyl ketone to a dihydrofuran d e r i v a t i v e f a l l s i n the category of a [1,3] sigmatropic s h i f t . Table XXII i l l u s t r a t e s the symmetry allowed processes a v a i l a b l e . The system at hand does not reveal as to whether the process i s a n t a r a f a c i a l or s u p r a f a c i a l . The r e s u l t s i n Table XXI, p. 97 regarding the stereo-chemistry of the rea c t i o n i n conjunction with a d e s c r i p t i o n of the symmetry allowed processes o u t l i n e d i n Table XXII requires that i f the reac t i o n i s concerted then the major pathway thermally involves an a n t a r a f a c i a l process with r e t e n t i o n of configuration at the migrating - 99 -Table XXII. Allowed Stereochemical Pathways f o r the Concerted Cyclopropyl Ketone-Dihydrofuran Conversion. Cyclopropyl Ketone Reaction Conditions cis-96 Ti. Ph * u trans-97 /\ / C O C H: Ph 36 P\A/ COCH, 37 A/ COCH, Ph 38 A hv A hv A hv s u p r a f a c i a l , i n v e r s i o n a n t a r a f a c i a l , r e t e n t i o n •f a n t a r a f a c i a l , i n v e r s i o n s u p r a f a c i a l , r e t e n t i o n s u p r a f a c i a l , i n v e r s i o n a n t a r a f a c i a l , r e t e n t i o n a n t a r a f a c i a l , i n v e r s i o n s u p r a f a c i a l , r e t e n t i o n a n t a r a f a c i a l , r e t e n t i o n s u p r a f a c i a l , i n v e r s i o n * s u p r a f a c i a l , r e t e n t i o n a n t a r a f a c i a l , i n v e r s i o n Major pathway carbon, a s i t u a t i o n which i s highly u n l i k e l y . 1 The major pathway f o r the photochemical process must occur s u p r a f a c i a l l y with retention of stereochemistry at the migrating center. Photochemical [1,3] sigmatropic s h i f t s have been observed i n several c a s e s 1 as a symmetry allowed s u p r a f a c i a l process with r e t e n t i o n Ref. (67), pages 121-122. - 100 -of configuration at the migrating center. The transition state for such a reaction i s easily accessible and imposes l i t t l e constraint since neither an antarafacial shift nor inversion at the migrating carbon i s required. However, the transition state that would then be required to explain the photochemical occurrence of the minor dihydrofuran product 97_ from 38 would involve both an antarafacial shift and inversion of stereochemistry. The construction of this transition state i s totally impossible owing to these constraints placed upon i t . The transition states for the thermal conversion to the dihydrofuran products are both f a i r l y strained because of the symmetry requirements imposed on the processes. To produce the major dihydrofuran an antara-f a c i a l process i s called for with retention at the migrating carbon, while the minor route must occur suprafacially with inversion of stereochemistry. Few thermal lj.3 sigmatropic shifts are known1 and then only when special constraints are already present. In view of the unfavourable, constraints placed upon the transition states i n the thermal rearrangement of a cyclopropyl ketone to a dihydrofuran i n which either an antarafacial process or an inversion of stereochemistry i s called for, i t seems unlikely that such a conversion occurs by a symmetry allowed concerted pathway. In the case of the photochemical rearrangement the major product i s explained nicely but the transition state for the minor product which may be as much as 15% i s not possible. For these reasons a non-concerted process is favoured. One of the observations made from Table XXI, p. 9 7 . 1 See previous footnote. - 101 -was the s i m i l a r i t y of the geometrical retention of the rearrangement whether the reaction occurred thermally or photochemically. This r e s u l t contains the i m p l i c a t i o n that both modes of re a c t i o n are s i m i l a r i n nature and that the reaction proceeds step-wise through a common intermediate. (c) The Step-Wise Reaction On turning to a step-wise mechanism, the problem of desc r i b i n g the exact nature of the intermediate i s very d i f f i c u l t . The longer the l i f e t i m e of t h i s intermediate the more rotations can occur and thus an i d e n t i c a l intermediate should be generated from the three cyclopropanes J36_, _3_7, and _38 leading to i d e n t i c a l r a t i o s of the dihydrof urans 97_ and 98_. As the l i f e t i m e decreases and r i n g closure becomes competitive with r o t a t i o n , then t h i s w i l l show up i n the product d i s t r i b u t i o n . This l a t t e r s i t u a t i o n i s the case both thermally and photochemically as noted i n Table XXI, p. 97 . Of course, the l i f e t i m e of the d i r a d i c a l i s not the only cause of concern i n the determination of the r e l a t i v e rates of c y c l i z a t i o n and r i n g closure. There i s also the energy b a r r i e r associated with the r o t a t i o n of the r a d i c a l centers; moreover, there i s the energy b a r r i e r f o r r i n g closure i t s e l f . However, the r e l a t i v e rates of c y c l i z a t i o n versus r o t a t i o n only p a r t l y describes the intermediate. This intermediate i s more f u l l y described i f some information can be derived about i t s behaviour with regard to r o t a t i o n a l preferences. Some information on t h i s aspect can be extracted from Tables X to XV, p. 63 to p. 68 which follow the - 102 -progress of tie conversion of the isomeric cyclopropyl ketones 36, 37 and _38 to the dihydrof urans 96_ and 97_ both thermally and photo-chemically. At the same time the c i s - t r a n s isomerization of the cyclopropanes i s monitored. The most i n s t r u c t i v e cyclopropane i s 3fi_ which has the C - l methyl, C-2 phenyl and C-3 methyl on the same side of the r i n g . On p y r o l y s i s at 285.0°, the cyclopropyl ketone 38. p r e f e r e n t i a l l y proceeds toward the cyclopropyl ketone _3_7 rather than 36 (Table XII, p. 65 ) eq. 65. Likewise, on the d i r e c t photolysis the same s i t u a t i o n i s even more g r e a t l y emphasized (Table XV, p. 68) eq. 65. The main reason f o r poi n t i n g out t h i s behaviour i s that i t i s s i m i l a r to the preferred r o t a t i o n observed from the s e n s i t i z e d p h o t o l y s i s of pyrazoline ^1 which has the same i n i t i a l geometry as cyclopropane 38. Pyrazoline _3_1, on s e n s i t i z e d p h o t o l y s i s , gives 90% of the cyclopropyl ketone 37^  but only 6% of the cyclopropane 36_, eq. 66. There Ph Me i s every reason to expect ( 9, 30, 34) the ^ to be the bond H Ac - 103 -broken i n cyclopropane 38., thus giving rise to the same diradical with the same rotational preferences that i s produced from pyrazoline 31. [66] n 37 (90%) 36 (6%) 31 Having shown from the experimental results that the intermediate species originating from different sources are somewhat similar, a rationalization can now be invoked to explain these results. Although many suggestions have been provided to explain cis-trans isomerization of cyclopropanes such as the trimethylene diradical (open chain) (24a, 25a,b) , the Smith mechanism (26) , and the trimethylene diradical ( TT-cyclopropane) (7), the most economical explanation appears to u t i l i z e the concept of a diradical that retains the integrity of the precursor (9a,c,36) s see Figure 21. These diradicals undergo conversion to one another by means of a s i n g l e r o t a t i o n at a time. This means that a process requiring a double inversion (i.e., 38 ->36) i s less l i k e l y to occur than a single inversion (i.e., 38 -»37) and that the net result of a double inversion can occur only by two successive single rotations. Such a mechanism has the merit in that i t does not require the exact nature of the diradical, only that i t retain the integrity of the precursor. A mechanistic scheme is presented i n Figure 21 for the conversion of the cyclopropyl ketones 36_, 37_, and 38 to the dihydrofurans 96_ and 97. - 104 -Figure 21. D i r a d i c a l mechanism (of In t e g r i t y ) f o r conversion of cyclopropyl ketones to dihydrofurans. The percentages are taken from Table XII, p. 63 and are those recorded a f t e r cyclopropane _38_ has been thermolyzed f or 3 min at 283.5°C. - 105 -This scheme (Figure 21) n i c e l y explains the main observations when the progress of the rearrangement of the cyclopropyl ketones 36_, 37_ and 3fi_ to the dihydrof urans cis-96 and trans-97 i s monitored (Tables X to XV, p. 63 to p. 68 ). The scheme accounts f o r the high degree of geometrical r e t e n t i o n f o r the cyclopropyl ketone to dihydrofuran conversion (Table XXI, p. 97 ). I t also explains the s i m i l a r i t y of the r e s u l t s with regard to the geometrical r e t e n t i o n of t h i s rearrangement whether the re a c t i o n occurs thermally or photo-chemically. Moreover, i t explains the preferred r o t a t i o n of the d i r a d i c a l intermediate produced when cyclopropane 38_ i s reacted e i t h e r thermally or photochemically i n that 38_ proceeds p r e f e r e n t i a l l y towards the cyclopropane _3_7 and not _36^  eq. 65. One can now return to the photochemical decomposition of the te t r a s u b s t i t u t e d 1-pyrazolines. In a s i m i l a r fashion, the idea of a 1, 3 - d i r a d i c a l that retains the i n t e g r i t y of i t s precursor can be u t i l i z e d . In t h i s instance, however, the precursor i s not a cyclopropane but rather a 1-pyrazoline. Taking pyrazolines 30_ to 3_3 as examples, a scheme o u t l i n i n g t h e i r decomposition to 1,3-diradicals and subsequent r i n g closure to cyclopropane products i s given i n Figure 22. This scheme n i c e l y explains the observed behaviour of the 1,3-d i r a d i c a l s formed from pyrazolines 30_ to _33. The product d i s t r i b u t i o n s , as p r e v i o u s l y 1 d i s c u s s e d , i n d i c a t e d that two major routes were a v a i l a b l e to t h i s d i r a d i c a l once formed. In review, the f i r s t route i s that i f ei t h e r cyclopropane 36_ or J7 can be formed d i r e c t l y ( r , r ) then t h i s pathway w i l l dominate. I f , however, a (r,r ) process would lead to e i t h e r 1 See page 95. - 106 -Figure 22. D i r a d i c a l mechanism (of i n t e g r i t y ) f o r the photochemical decomposition of t e t r a s u b s t i t u t e d 1-pyrazolines. - 107 -cyclopropane J38_ or 39, then a s i n g l e r o t a t i o n w i l l take place so as to y i e l d e i t h e r J7_ or 36 This s i n g l e r o t a t i o n occurs as a ( r , i ) process i n v o l v i n g the r a d i c a l center s u b s t i t u t e d with a phenyl and a hydrogen. The two remaining processes ( i , r ) and ( i , i ) play only a minor r o l e . A s i m i l a r scheme that would be consistent with the experimental r e s u l t s can be out l i n e d f o r pyrazolines J34_ and 3 5 . As f a r as the d i r e c t photolysis of the pyrazolines _30_ to 36_ i s concerned, again, the same type of scheme i n p r i n c i p l e w i l l s a t i s f y the experimental r e s u l t s since the d i r a d i c a l s produced upon d i r e c t photolysis do not have to undergo spin i n v e r s i o n before r i n g closure can occur. This r e f l e c t s a shorter l i f e t i m e of the d i r a d i c a l g i v i n g less opportunity f o r s i n g l e r o t a t i o n s to take place and therefore l e s s progression i n the r e a c t i o n (see Table XX, p. 92 ). Such a scheme that i s used f o r both the d i r e c t and s e n s i t i z e d photolyses w i l l always imply that the d i r e c t p h o t o l y s i s w i l l proceed so as to give more of the cyclopropane with retention of the geometry present i n the s t a r t i n g pyrazoline. As expressed before, t h i s i s not always the case with a l k y l substituted 1-pyrazolines (8b) (see pyrazolines 70 , 7 1 , and 2 2 , Table XIX, p. 87. By examining the i n i t i a l r a t i o of products f o r the thermolysis of cyclopropane _38, a crude estimate can be made of the r e l a t i v e rates of some of the reactions i n the scheme ou t l i n e d i n Figure 2 1 , p. 104. Figure 21 shows the percentage of each compound a f t e r cyclopropane 38_ has been thermolyzed at 283.5°C for 3 minutes. 1 These percentages 1 Taken from Table XII, p. 6 5 . - 108 -i n d i c a t e that a f t e r the d i r a d i c a l 37-a i s formed that i t r i n g closes to the cyclopropane 37_ about 1.2%/.03% + . 1% - 9 times f a s t e r than i t proceeds i n t o t a l to the dihydrofuran trans - 9 7 and the cyclopropane 36. This i n turn means that when the d i r a d i c a l 37-a i s produced thermally from the cyclopropane 37_ that the major consequence of 37-a i s the return to _3_7, an event which i s a chemically i n e f f e c t i v e , "no re a c t i o n " r e a c t i o n (36 ) . This statement i s given support by the d i s t r i b u t i o n of products obtained when pyrazoline 30, which i s expected to produce the same d i r a d i c a l 37-a, i s photolyzed (see Figure 2 2 , p. 1 0 6 ) . Direct photolysis of 30_ y i e l d s 37_ as the sole cyclopropane with no dihydrofuran formation. S e n s i t i z e d p h o t o l y s i s of J30 gives the cyclopropanes _3_7 and _36_ i n 98 and 2% r e s p e c t i v e l y , and again no dihydrofuran i s formed (see Table XX, p. 9 2 ) . The schemes i n v o l v i n g a d i r a d i c a l mechanism (of i n t e g r i t y ) i n Figure 21 and 2 2 , p. 104 and p. 1 0 6 , are presented i n order to i l l u s t r a t e the pathways adopted when the cyclopropyl ketones j36_, 37_ and _38 are treated e i t h e r thermally or photochemically, or when the tet r a s u b s t i t u t e d pyrazolines to J33_ are decomposed photochemically to y i e l d cyclopropane and dihydrofuran products. There i s , however, an i n t e r e s t i n g observation not taken i n t o account by the schemes presented i n Figures 21 and 2 2 , p. 104 and p. 106. Although the d i r a d i c a l s produced by d i f f e r e n t sources do show s i m i l a r r o t a t i o n a l preferences i n cyclopropane isomerization and s i m i l a r retention of geometry i n the r i n g expansion reaction to dihydrofurans, they must, however, be generated with a v a r i e t y of energies. This i s evident when neither thermolysis nor d i r e c t photolysis - 109 -of the cyclopropane _36_ produces any of the c t , g - or 3 ,y-unsaturated ketones 120 and 131, eq. 58, p. 72 . On the other hand, the cyclopropyl ketones 3_7 and ^ 38_ do not y i e l d o l e f i n s thermally, but on d i r e c t photolysis _3_7 and _3_8 give o l e f i n s i n s u b s t a n t i a l amounts. The pyrazolines 30_ to 33^ , which are expected to give the same d i r a d i c a l intermediate as the one produced by the thermolysis and photoly s i s of cyclopropanes 36_, 37_, and _38, give no o l e f i n s e i t h e r by d i r e c t or s e n s i t i z e d p h o t o l y s i s . (d) K i n e t i c Studies The need for a k i n e t i c study of the cyclopropyl ketone-dihydrofuran interconversion became apparent with the observation that the r a t i o of the dihydrofuran products (96 and 97) to that of the y,5-unsaturated ketones (123 and 124) was dependent to a large extent on the temperature at which cyclopropyl ketone 36 was thermolyzed, eq. 67, see Table XXIII f o r r a t i o of products. - 110 -In the case of the cyclopropyl ketone J36_ the two reactions are competing. The r i n g opening reaction i s the r e s u l t of the C - l a c e t y l and C :-3 methyl being i n a c i s o r i e n t a t i o n , t h i s s i t u a t i o n permitting formation of the y»6-unsaturated ketones 123 and 124 i n a f i r s t order r e a c t i o n (70). Table XXIII. P y r o l y s i s of the Cyclop 1 2 Temperatures. ' ropyl Ketone 36 at D i f f e r e n t Temperature R a t i o 1 of Difference i n ^ (°C) O : v>6 0 (96+97):(123+124) A c t i v a t i o n Parameters 255.5 27:73 AAHf = 13.5 kcal/mole 272.0 40:60 A log A = 2.95 292.0 45:55 AAS + = 24 e.u. 312.7 55:45 333.0 69:31 The values are taken from Table X. Derivation of parameters are i n Appendix 4. The Arrhenius p l o t i s contained i n Appendix 5. From Table XXIII i t can be seen that at low temperatures the y,6-unsaturated ketones are the major products. However, as the temperature i s r a i s e d the proportion of dihydrofuran i n the product i s remarkably - I l l -increased. Such a trend i s i n d i c a t i v e of two competiting reactions that have widely d i f f e r e n t a c t i v a t i o n parameters. In t h i s p a r t i c u l a r instance, the dihydrofuran forming reaction w i l l l i k e l y have both a la r g e r energy of a c t i v a t i o n and a more p o s i t i v e entropy of a c t i v a t i o n . Knowing the r a t i o of the products for at l e a s t two temperatures allows f o r the calculation of the d i f f e r e n c e s i n AH' and log A of the two reactions. Calculations reveal that the dihydrofuran re a c t i o n has both a l a r g e r AH^ by 13.5 kcal/mole and a l a r g e r log A by 2.95 or 24 entropy u n i t s , Table XXIII. Analogous reactions to the rearrangement of a cyclopropyl ketone to y,6-unsaturated ketones have been reported with t h e i r k i n e t i c data. One study involved the rearrangement of cyclopropane d e r i v a t i v e s having a carbomethoxy function c i s to an a l k y l substituent (68). The re a c t i o n i s f i r s t order and proceeds with a AH 1 of between 25 to 38 kcal/mole with a AS**" ranging from -8 to -37 e.u. These r e s u l t s support a concerted t r a n s f e r of hydrogen i n a t i g h t l y bound rate determining t r a n s i t i o n state. Another analogous s i t u a t i o n e x i s t s i n the case of cyclopropanes which have a v i n y l and methyl i n a c i s arrangement (69a,b). Again, t h i s r e a c t i o n proceeds with a f a i r l y low a c t i v a t i o n energy and a negative entropy of a c t i v a t i o n . As f o r cyclopropyl ketones, k i n e t i c data have been reported f o r l-acetyl-2,2-dimethyl cyclopropane 141 which undergoes rearrangement to the y,6-unsaturated ketone 142 with a heat of a c t i v a t i o n of 30 kcal/mole and an entropy of a c t i v a t i o n of -10 e.u., eq. 68 (70). - 112 -[68] 141 142 Knowing that the rearrangement i n eq. 68 has values of AH = 30 kcal/mole and AS^ = -10 e.u., then a very rough expectation f o r the dihydrofuran r e a c t i o n i n eq. 67 might be an a c t i v a t i o n energy of 30 + 13.5 = 43.5 kcal/mole and an entropy of a c t i v a t i o n of -10 + 24 = +14 e.u. Such a crude c a l c u l a t i o n cannot be expected to be accurate since there i s undoubtedly a f l u c t u a t i o n of a c t i v a t i o n parameters for the r i n g opening process for cyclopropyl ketones j u s t as there i s i n the case of esters (68). Nevertheless, the values obtained by such a comparison should i n d i c a t e the general range f o r the a c t i v a t i o n energy of about 44 kcal/mole and a near zero or p o s i t i v e entropy of a c t i v a t i o n f o r the conversion of the cyclo propyl ketone 36_ to the dihydrof urans 96_ + 97. The system chosen f o r a k i n e t i c study involved the conversion of the cyclopropyl ketones 132 and 133 to the dihydrofuran 136, eq. 69. - 1 1 3 -The cyclopropyl ketones 132 and 133 with the absence of the methyl group at C -3 are otherwise s i m i l a r i n structure to the cyclopropyl ketones 36_, _3_7 and _38. Rates were measured over a temperature range of 32.6° from 254.9° to 287.5°C. A l e a s t squares p l o t gave an a c t i v a t i o n energy E = 4 8 . 1 kcal/mole and a log A of 14 .9 (AS' = +6.4 e.u.), see Table XVII, p. In addition, attempts were made to measure the rates of c i s - t r a n s isomerization of the isomeric cyclopropyl ketones 132 and 133 so that these a c t i v a t i o n parameters could be compared to those found f o r the conversion of the same cyclopropanes to the dihydrofuran 136. Regrettably, the k i n e t i c data obtained f o r the c i s - t r a n s isomerization were not reproducible. Nevertheless, one u s e f u l r e s u l t found i s that the c i s - t r a n s isomerization occurs much f a s t e r than the conversion of the cyclopropanes to the dihydrofuran 136. The c i s - t r a n s r e a c t i o n took place i n the measureable range of approximately 200 to 235°C; whereas, the range used to study the cyclopropyl ketone-dihydrofuran interconversion was at the much higher range of 255 to 290°C. I t i s estimated that the rates of the two processes d i f f e r by one to two powers of ten, with the c i s - t r a n s isomerization being the f a s t e r r e a c t i o n . A mechanistic scheme i s presented i n Figure 2 3 . In a previous s e c t i o n (part 2(b) of the Discussion, p. 98 ) dealing with the formation of the dihydrofuran 96_ and 97_ from the cyclopropyl ketones 36_, J37 and J38_ step-wise mechanism was favoured over a concerted process. This conclusion was reached on the basis of the unfavourable constraints placed upon the t r a n s i t i o n states by the symmetry allowed - 114 -132 132-a 133-a 133 Figure 23. D i r a d i c a l mechanism (of i n t e g r i t y ) f o r the interconversion of the cyclopropyl ketone 132 + 133 and dihydrofuran 136. processes, p a r t i c u l a r l y those t r a n s i t i o n states i n v o l v i n g an antara-f a c i a l s h i f t or those proceeding with i n v e r s i o n of the migrating center (see Table XXII, p. 99 ). In add i t i o n , both the thermal and photochemical rearrangement of any one of the cyclopropyl ketones 36, 37 or 38i proceeded with almost i d e n t i c a l r e s u l t s with respect to the percentage of dihydrofuran formation occurring with r e t e n t i o n of geometry (see Table XXI, p. 97 ). This r e s u l t suggested that both modes of reaction are s i m i l a r i n nature and that the reaction occurs step-wise through a common intermediate. A step-wise r e a c t i o n (part 2(c) of the Discussion, p. 101 ) using d i r a d i c a l s which were formed while r e t a i n i n g the i n t e g r i t y of i t s - 115 -precursor was used to explain the r e s u l t s . This scheme (Figure 21, p. 104 ) n i c e l y explains the high degree of geometrical retention for the dihydrofuran formation. In a d d i t i o n , i t also accounts f o r the s i m i l a r i t y of the r e s u l t s with regard to the geometrical r e t e n t i o n of t h i s rearrangement whether the r e a c t i o n occurs thermally or photo-chemically. Moreover, i t explains the preferred r o t a t i o n of the d i r a d i c a l intermediate produced from cyclopropane 38_ when treated e i t h e r thermally or photochemically. For the above mentioned reasons, a scheme (Figure 23, p.H4 ) invoking a step-wise mechanism u t i l i z i n g d i r a d i c a l s which r e t a i n the i n t e g r i t y of the cyclopropane precursor i s used f o r the conversion of the cyclopropyl ketones 132 and 133 to the dihydrofuran 136. This system does not provide any information about the degree of geometrical r e t e n t i o n for the dihydrofuran formation or about r o t a t i o n a l preferences of the d i r a d i c a l . In t h i s instance, however, i t was observed that the c i s - t r a n s isomerization of the cyclopropanes 132 and 133 took place one to two powers of ten f a s t e r than the dihydro-furan forming reaction. Moreover, the k i n e t i c study revealed a high a c t i v a t i o n energy of 48.1 kcal/mole f o r dihydrofuran formation. These r e s u l t s are consistent with a rate determining t r a n s i t i o n s tate for the dihydrofuran forming r e a c t i o n between the d i r a d i c a l and the dihydro-furan. This s i t u a t i o n i s analogous to the vinylcyclopropane-cyclopentene rearrangement i n which the rate determining t r a n s i t i o n state f o r cyclopentene i s placed between the d i r a d i c a l and cyclopentene (25a). - 116 -To conclude, a b r i e f word should be s a i d about the thermal decomposition of the t e t r a s u b s t i t u t e d 1-pyrazolines (Table XX, p. 92). For the d i r e c t and s e n s i t i z e d photolysis of ttese pyrazolines, a mechanistic scheme (Figure 22, p. 106) invoking d i r a d i c a l s which r e t a i n the i n t e g r i t y of the pyrazoline precursor was used to explain the product d i s t r i b u t i o n s . ^ However, the product d i s t r i b u t i o n s from the thermal decomposition of the t e t r a s u b s t i t u t e d 1-pyrazolines do not f i t t h is scheme. This r e s u l t suggests that on going from the thermolysis to the photolysis of pyrazolines that there i s a major change i n mechanism i n which the thermal decomposition involves a route not accounted for i n the scheme outlined i n Figure 22. - 117 -IV. EXPERIMENTAL 1. General Statement Infrared ( i . r . ) spectra were recorded on a Perkin-Elmer Model 457 spectrometer. A l l spectra were measured as a l i q u i d f i l m using sodium chl o r i d e p l a t e s . Melting points (m.p.) and b o i l i n g points (b.p.) are uncorrected. U l t r a v i o l e t (ii.v.) spectra were recorded on a Carey 15 spectrometer. The 60 MHz nuclear magnetic resonance (n.m.r.) spectra were recorded on \arian Associates Model A-60 spectrometer. The 100 MHz n.m.r. spectra were recorded on a Varian Associates HA-100 or XL-100 spectrometer. Tetramethylsilane was used as an i n t e r n a l standard unless otherwise noted. The vapour phase chromatography (v.p.c.) units used were an Aerograph Model A-90-P and a Perkin-Elmer 226. In the former instrument columns of 10* x 1/4" were used unless otherwise noted. In the l a t t e r , columns of 150' x .01" i . d . were used. The spinning band apparatus employed was a Nester-Faust s t a i n l e s s s t e e l (10 mm x 24"). Petroleum ether r e f e r s to the f r a c t i o n b o i l i n g between 30-60°. The petroleum ether was d i s t i l l e d before use i n column chromatography. - 118 -2. Preparation of S t a r t i n g Materials (a) 3-Methyl-3-pentene-2-one, (Z)-(IOO) I r r a d i a t i o n of 30 g of 3-methyl-3-pentene-2-one, (E)-(100) (Aldrich) e i n 500 ml of ether f o r 4 days i n a s i l i c a tube at 3100 A (Rayonet Reactor) res u l t e d i n a 25% conversion to the Z-100 as determined by v.p.c. (20% Dinonyl phthalate, 133°, 30 ml/min). The r e t e n t i o n times f o r the Z_ and E_ isomers were 7.0 and 9.6 min r e s p e c t i v e l y . Preparative V.p.c. gave the desired Z_ isomer i n greater than 95% p u r i t y . For the ketone Z-100; i . r . bands at 1668, 1360, 1272, and 1132 cm"1. (b) 3-Methyl-3-phenyl-3-butene-2-one, (E)-(102) The o l e f i n 102 was prepared according to the procedure of Noyce (71). (c) Benzaldehyde hydrazone The t i t l e compound was prepared by a modified procedure of Curtius (72) as described by McGreer (15). Cd) N-Nitroso-N-methyl-urea The t i t l e compound was prepared by the procedure given i n Organic Syntheses (73). (e) N-Nitroso-N-ethyl-urea The t i t l e compound was prepared according to the method of Chiu (74). - 119 -(f) Diazomethane arid diazoethane Diazomethane and diazoethane were prepared N-nitroso-N-methyl urea and N-nitroso-N-ethyl urea respectively according to the method described by Chiu (74). Cg) Phenyldiazomethane The t i t l e compound was prepared according to the modified procedure of Staudinger (75) as modified by McGreer (15). 3. Cis-3,4-dimethyl-3-acetyl-l-pyrazoline (98) (a) Preparation and identification To an ether solution of 6.0 g (0.061 mole) of 3-methyl-3-pentene-2-one, (jE)-(100) was added diazomethane prepared from 15.45 g (0.174 mole) of N-nitroso-N-methyl urea. The resulting solution was l e f t at room temperature for one week. Removal of the ether by rotatory evaporation gave 8.25 g of a clear yellow solution. Bulb to bulb d i s t i l l a t i o n (bath temperature 65-75°) at 0.5 mm Hg gave 7.10 g (0.051 mole) of a clear colourless liquid. The yield of the pyrazoline 98 from the starting olefin 100 was 84%. For the pyrazoline £8: i . r . 1542 cm - 1 (N=N stretch); u.v. (EtOH) 336 my (e = 271); n.m.r. (60 MHz, CC1 4) 7.68 and 8.76 x (singlets, acetyl methyl and C-3 methyl respectively, 9.06 x (doublet J - 7.2 Hz) C-4 methyl, 8.96 x (multiplet) C-4 hydrogen, 5.37 x (doublet of doublets J - 17.8 and 8.6 Hz) one C-5 hydrogen, 6.18 x (doublet of doublets J = 17.8 and 7.8 Hz) other C-5 hydrogen. - 120 -Anal. Calcd. f o r c 7 H 1 2 O N 2 : C ' 5 9 , 9 7 ; H> 8 ' 6 3 , F o u n d : c» 60.30; H, 8.73. (b) P y r o l y s i s and product i d e n t i f i c a t i o n The p y r o l y s i s of pyrazoline 98_ was c a r r i e d out e i t h e r as a neat sample i n a sealed pyrex tube (100 mm x 2.4 mm i.d.) or as a neat sample i n the i n j e c t o r of the v.p.c. The v.p.c. (5% Carbowax-15% QF-1, 125°, 30 ml/min) showed four peaks with r e t e n t i o n times of 2.5, 3.6, 4.2, and 5.2 minutes. The 2.5 min peak was i s o l a t e d by preparative v.p.c. and i d e n t i f i e d by n.m.r. as 2,3,4-trimethyl-4,5-dihydrofuran (111). For the dihydrofuran 111: i . r . bands at 1707, 1688 and 999 cm"1. The 3.6 and 4.2 min peaks were i s o l a t e d together by preparative 'V.p.c. The former was i d e n t i f i e d as 3,4-dimethyl-4-pentene-2-one (113) by n.m.r. For the 8,y-o l e f i n 113: n.m.r. (60 MHz, CCl^) 5.10 T (narrow mu l t i p l e t ) C-5 v i n y l hydrogens, 6.84 T (quartet J = 7.0 Hz) C-3 hydrogen, 7.95 T ( s i n g l e t ) C - l a c e t y l methyl, 8.33 T ( s i n g l e t showing long range coupling) C-4 methyl, 8.88 T (doublet J = 7.0 Hz) C-3 methyl. The l a t t e r peak was i d e n t i f i e d by n.m.r. as trans-1,2-dimethyl-l-a c e t y l cyclopropane (115). For the cyclopropane 115: (60 MHz, CCl^) 7.84 and 8.62 x ( s i n g l e t s ) a c e t y l and C - l methyls r e s p e c t i v e l y . The 5.2 min peak was i s o l a t e d by preparative v.p.c. and was found by n.m.r. to consist of two compounds. The major component was i d e n t i f i e d as 3,4-dimethyl-3-pentene-2-one (112) by i t s n.m.r. spectrum. For the ct,g-olefin 112: n.m.r. (60 MHz, CCl^) 7.86 T ( s i n g l e t ) a c e t y l methyl, 8.16 x ( s i n g l e t of i n t e n s i t y 6) C-5 hydrogens, 8.26 x ( s i n g l e t - 121 -showing long range coupling) C-3 methyl. The minor component of peak D was i d e n t i f i e d by n.m.r. as c i s -1,2-dimethyl-l-acetyl cyclopropane (114). For the cyclopropane 114: n.m.r. (60 MHz, CCl^) 8.00 T (s i n g l e t ) a c e t y l methyl, 8.71 x ( s i n g l e t ) C - l methyl. The r a t i o of the o l e f i n 112 and the cyclopropane 114 was found by n.m.r. to be 4:1 r e s p e c t i v e l y . (c) Direct photolysis and product i d e n t i f i c a t i o n A general d e s c r i p t i o n of the experimental procedure i s given i n the Experimental § 9.1 incl u d i n g the experimental d e t a i l s f o r i n d i v i d u a l runs i n Table XXX. The v.p.c. (5% Carbowax-15% QF-1, 125°, 30 ml/min) of the reaction products showed f i v e peaks of re t e n t i o n times 2.5, 3.6, 4.2, 4.9, and 5.2 minutes. The 2.5 min peak was present i n a trace amount and thus was not i s o l a t e d . I t was i d e n t i f i e d as 2,3,4-trimethyl-4,5-dihydrofuran (111) on the basis of i t s v.p.c. r e t e n t i o n time. The 3.6 min peak was i s o l a t e d by preparative v.p.c.a nd i d e n t i f i e d by i . r . as 3-methyl-3-pentene-2-one, (Z)-(100). For the ketone Z-100: i . r . bands at 1690, 1623, 1230 and 967 cm"1. The 4.2 min peak accounted f o r about 1% of the product and was i d e n t i f i e d as trans-1,2-dimethyl-l-acetyl cyclopropane (115) on the basis of i t s v.p.c. retention time. The 4.9 min peak was i s o l a t e d by preparative v.p.c. as an enriched mixture containing the 5.2 min peak as an impurity. The former was i d e n t i f i e d as the s t a r t i n g o l e f i n 3-methyl-3-pentene-2-one (E)-(IOO) by n.m.r. For the ketone 100: n.m.r. (60 MHz, CC1,, u c e l l , - 122 -external TMS) 7.82 x (s i n g l e t ) a c e t y l methyl, 3.22 x (quartet J = 7.3 Hz) C-4 v i n y l hydrogen.. The 5.2 min peak was i s o l a t e d by preparative v.p.c. and i d e n t i f i e d as c i s - l , 2 - d i m e t h y l - l - a c e t y l cyclopropane (114) by i . r . and n.m.r. For the cyclopropane 114: i . r . 1687, 1278, 1156, and 821 cm - 1; n.m.r. (60 MHz, CCl^, external TMS) 8.00 x ( s i n g l e t ) a c e t y l methyl, 8.72 x ( s i n g l e t ) C - l methyl, 9.73 x (multiplet) one of r i n g hydrogens. (d) S e n s i t i z e d p h o t o l y s i s and product i d e n t i f i c a t i o n A general d e s c r i p t i o n of the experimental procedure i s given i n the Experimental § 9(b) in c l u d i n g Table XXXI which contains experimental d e t a i l s f o r i n d i v i d u a l runs. The v.p.c. (5% Carbowax-15% QF-1, 125°, 30 ml/min) of the reac t i o n products showed 3 peaks with retention times of 2.4, 4.5, and 6.8 minutes. The 2.4 and 4.5 min peaks were i d e n t i f i e d as 2,3,4-trimethyl-4,5-dihydrofuran (111) and trans-1,2-dimethyl-l-acetylcyclopropane (115) re s p e c t i v e l y on the basis of t h e i r v.p.c. r e t e n t i o n times. The 6.8 min peak was the major product and was i d e n t i f i e d as c i s - l , 2 - d i m e t h y l - l - a c e t y l cyclopropane (114) by i t s n.m.r. spectrum. For the cyclopropane 114: n.m.r. (60 MHz, CCl^, external TMS) 8.28 x (si n g l e t ) a c e t y l methyl, 9.00 x ( s i n g l e t ) C - l methyl, 10.00 x (multiplet) one of r i n g hydrogens. The n.m.r. i s that of the crude r e a c t i o n mixture with the s e n s i t i z i n g agent benzophenone present. - 123 -(e) D i s t r i b u t i o n of products TABLE XXIV. D i s t r i b u t i o n 1 of Products from the Decomposition of c i s -3,4-dimethyl-3-acetyl-1-pyrazoline. Conditions s.m. d.h.f. By trans-A aB cis-A 152 182^ 230 : 5 hv-d hv-s" 0 0 0 13 0 6 9 7 tr. 3 6 5 5 0 0 10 13 25 1 5 62 16 58 15 63 4 0 86 0 91 by at l e a s t 3 runs by v.p.c. neat p y r o l y s i s . p y r o l y s i s i n i n j e c t o r of v.p.c. the r a t i o of 112:114 was not determined. see Experimental 9(a) and 9(b) for d e t a i l s of i n d i v i d u a l experiments. 4. Trans_-3,4-dimethyl-3-acetyl-1-pyrazoline (99) (a) Preparation and i d e n t i f i c a t i o n To an ether s o l u t i o n of 0.84 g (.0086 mole) of 3-methyl-3-pentene-2-one, (Z)-(IOO) was added diazomethane prepared from 4.55 g (0.044 mole) of N-nitroso-N-methyl urea. The s o l u t i o n was l e f t f o r 10 days at room temperature. Removal of the ether by rotatory evaporation gave 1.26 g of a s l i g h t l y c l e a r yellow s o l u t i o n . Bulb to bulb d i s t i l l a t i o n - 124 -(bath temp. 60-70°) of a cl e a r colourless l i q u i d . The y i e l d from the s t a r t i n g o l e f i n 100 was 87%. For the pyrazoline 99_: i . r . 1546 cm - 1 (N=N s t r e t c h ) ; u.v. (EtOH) 341 my e = 245; n.m.r. (60 MHz, CCl^) 7.78 and 8.25 T ( s i n g l e t s ) a c e t y l methyl and C-3 methyl r e s p e c t i v e l y , 9.30 x (doublet J = 7.0 Hz) C-4 methyl, 8.16 x (multiplet) C-4 hydrogen, 5.52 x (doublet of doublets) one of C-5 hydrogens, 5.83 x (doublet of doublets) other C-5 hydrogen. The two doublet of doublets for the C-5 hydrogens have approximate coupling constants of J = 17 and 4 Hz. Anal. Calcd. f o r C ^ ^ O N ^ C, 59.97; H, 8.63. Found: C, 59.88; H, 8.73. (b) P y r o l y s i s and product i d e n t i f i c a t i o n The p y r o l y s i s of pyrazoline 99_ was c a r r i e d out e i t h e r as a neat sample in a scaled pyrex tube (1.2 x 100 mm) or as a neat sample i n the i n j e c t o r of the v.p.c. The v.p.c. (5% Carbowax-15% QF-1, 125°, 20 ml/min) showed four peaks with retention times of 2.9, 3.7, 4.1 and 5.8 minutes. The 2.9 min peak was i s o l a t e d by preparative v.p.c. and i d e n t i f i e d by Ir. and n.m.r. as 2,3,4-trimethyl-4,5-dihydrofuran (111). For the dihydrofuran 111: i . r . band at 1706 cm 1 (C=C s t r e t c h ) ; n.m.r. (60 MHz, CCl^) 5.76 and 6.40 x (multiplets resembling t r i p l e t s with J = 8-9 Hz approximately) C-5 hydrogens, 7.22 x (multiplet) C-4 hydrogen, 8.32 and 8.44 x ( s i n g l e t s showing long range coupling) C-2 and C-3 methyls, 8.98 x (doublet J = 7.0 Hz) C-4 methyl. The 3.7 and 4.1 min peaks were i s o l a t e d together by preparative - 125 -v.p.c. The former peak was i d e n t i f i e d as 3,4-dimethyl-4-pentene-2-one (113) by i . r . and n.m.r. For the 8,y - o l e f i n 113: i . r . 1714 cm 1 (C=0 stretch) and 1642 cm"1 (C=C s t r e t c h ) ; n.m.r. (60 MHz, CCI 4) 5.10 T (narrow multiplet) C-5 v i n y l hydrogens, 6.83 x (quartet J = 7.0 Hz) C-3 hydrogen, 7.96 x ( s i n g l e t ) a c e t y l methyl, 8.43 x ( s i n g l e t showing long range coupling) C-4 methyl, 8.88 x (doublet J = 7.0 Hz) C-3 methyl. The l a t t e r peak was i d e n t i f i e d by i.r.and n.m.r. as trans-1,2-dime t h y l - l - a c e t y l cyclopropane (115). For the cyclopropane 115: i . r . 1692 cm"1 (C=0 s t r e t c h ) ; n.m.r. (60 MHz, CCl^) 7.82 and 8.62 x (si n g l e t s ) a c e t y l and C - l methyls r e s p e c t i v e l y , 9.40 x (multiplet) one of r i n g hydrogens. The 5.8 min peak was i s o l a t e d by preparative v.p.c. and was found by n.m.r. to consist of two compounds. The major component was i d e n t i f i e d by i t s n.m.r. spectrum as 3,4-dimethyl-3-pentene-2-one (112). For the a , 8 - o l e f i n 112: n.m.r. (60 MHz, CCl^) 7.84 x (s i n g l e t ) a c e t y l methyl, 8.16 x ( s i n g l e t ) C-5 hydrogens, 8.24 x ( s i n g l e t showing long range coupling) C-3 methyl. The minor component was i d e n t i f i e d by n.m.r. and i . r . as cis-1,2-dimethy1-1-acetyl cyclopropane. For the cyclopropane 114: n.m.r. (60 MHz, CCl^) 7.88 x ( s i n g l e t ) a c e t y l methyl, 8.68 x ( s i n g l e t ) C - l methyl. The i . r . spectrum of the 5.8 min peak showed a s i n g l e C=0 s t r e t c h at 1686 cm"1. The r a t i o of the o l e f i n 112 and the cyclopropane 114 was found by n.m.r. to be 3:2 r e s p e c t i v e l y . - 126 -(c) Direct photolysis and product i d e n t i f i c a t i o n A general d e s c r i p t i o n of the experimental procedure i s given i n the Experimental §9(a), i n c l u d i n g the experimental d e t a i l s f o r i n d i v i d u a l runs i n Table XXX. The v.p.c. (5% Carbowax-15% QF-1, 125°, 30 ml/min) showed four peaks of ret e n t i o n times 3.5, 4.1, 4.8, and 6.0 minutes. The 3.5 and 4.8 min peaks accounted f o r about 2% of the r e a c t i o n products and thus were not i s o l a t e d . They were i d e n t i f i e d as 3-methyl-3-pentene-2-one, (Z)-(100) and, (E)-(100) r e s p e c t i v e l y on the basis of t h e i r v.p.c. r e t e n t i o n times. The 4.1 min peak was the major product and was i s o l a t e d by preparative v.p.c. and i d e n t i f i e d by i . r . and n.m.r. as trans-1,2-di m e t h y l - l - a c e t y l cyclopropane (115). For the cyclopropane 115: i . r . bands at 1691, 1358, 1149, and 829 cm"1; n.m.r. (60 MHz, CCl^,) 7.86 T ( s i n g l e t ) a c e t y l methyl, 8.63 x ( s i n g l e t ) C - l methyl, 9.05 x (multiplet) C-2 methyl, 9.58 x (multiplet)one of r i n g hydrogens. The 6.0 min peak was i s o l a t e d by preparative v.p.c. and i d e n t i f i e d by i . r . as c i s - l , 2 - d i m e t h y l - l - a c e t y l cyclopropane (114). For the cyclopropane 114; i . r . bands at 1689, 1276, 965 and 822 cm"1. (d) S e n s i t i z e d photolysis and product i d e n t i f i c a t i o n A general d e s c r i p t i o n of the experimental procedure i s given i n the Experimental §9(b) i n c l u d i n g Table XXXI which contains experimental d e t a i l s f o r i n d i v i d u a l runs. The v.p.c. (5% Carbowax-15% QF-1, 125°, 30 ml/min) of the reaction products showed 3 peaks with r e t e n t i o n times of 2.5, 4.6 and 7.0 min. - 127 -The 2.5 min peak was i d e n t i f i e d as 2,3,4-trimethyl-4,5-dihydro-furan (111) on the basis of i t s v.p.c. retention time. The 4.6 and 7.0 min peaks were i d e n t i f i e d by n.m.r. as trans-and cis-1,2-dimethyl-l-acetyl-cyclopropane (115) and (114), r e s p e c t i v e l y . For the trans-cyclopropane 115: n.m.r. (60 MHz, CCl^, i n t e r n a l TMS) 7.92 x (s i n g l e t ) a c e t y l methyl. For the cis-cyclopropane 114: 8.08 x (s i n g l e t ) a c e t y l methyl, 9.80 x (multiplet) one of r i n g hydrogens. The n.m.r. i s that of the crude re a c t i o n mixture with the s e n s i t i z i n g agent benzophenone present. (e) D i s t r i b u t i o n of products Table XXV. D i s t r i b u t i o n 1 of Products from the Decomposition of Trans-3,4-dimethyl-3-acetyl-l-pyrazoline. Conditions s.m. d.h.f. By trans-A ctB cis-A 152° 2 0 18 4 33 18 27 230° 2 0 19 5 31 45 4 h - d 5 2 0 0 75 0 23 h - s 5 0 4 0 15 0 82 1 by at l e a s t 3 runs by v.p.c. neat p y r o l y s i s 3 p y r o l y s i s i n i n j e c t o r of v.p.c. 4 the r a t i o of 112:114 was not determined 5 See Experimental § 9(a) and § 9(b) for d e t a i l s of i n d i v i d u a l experiments. - 128 -5. C i s - and Trans-3,5-dimethyl-3-acety1-1-pyrazolines (19) and (20) (a) Preparation The t i t l e compounds were prepared according to the procedure of Chiu (4). Addition of diazoethane prepared from 66 g (0.563 mole) of N-nitroso-N-ethyl urea to 10.6 g (0.126 mole) of f r e s h l y d i s t i l l e d methyl isopropenyl ketone gave a f t e r vacuum d i s t i l l a t i o n 12.8 g (0.92 mole) f o r a 73% y i e l d . The n.m.r. spectra i n d i c a t e d the r a t i o of the pyrazolines 19:20 to be 2:3. A spinning band d i s t i l l a t i o n on the d i s t i l l a t e from the simple d i s t i l l a t i o n followed. This gave the r a t i o of the low b o i l i n g c i s -pyrazoline 19_ to the high b o i l i n g trans-pyrazoline 20 of 5:95. For the trans-pyrazoline 20: n.m.r. (60 MHz, CCl^) 5.49 T (sextet with J = 7.6 Hz) C-5 hydrogen, 7.64 T ( s i n g l e t ) a c e t y l methyl, 8.46 x (doublet J = 6.8) C-5 methyl, 8.62 x (s i n g l e t ) C - l methyl. A second spinning band d i s t i l l a t i o n using a f r a c t i o n from the f i r s t spinning band d i s t i l l a t i o n containing the pyrazolines i n a 1:1 r a t i o was performed. This gave the r a t i o of the low b o i l i n g c i s -pyrazoline:trans-pyrazoline of 80:20. For the c i s - p y r a z o l i n e 19: n.m.r. 5.65 x (sextet with J = 7.8 Hz) C-5 hydrogen, 7.57 x (doublet of doublets J = 13.0 and 8.6 Hz) one C-4 hydrogen, 9.32 x (doublet of doublets J = 13.0 and 7.6 Hz) other C-4 hydrogen, 7.75 x ( s i n g l e t ) a c e t y l methyl, 8.52 x (doublet J = 7.2 Hz) C-5 methyl, 8.39 x ( s i n g l e t ) C-3 methyl. - 1 2 9 -(b) S e n s i t i z e d photolysis and product i d e n t i f i c a t i o n A general d e s c r i p t i o n of the experimental procedure i s given i n Experimental § 9(b) i n c l u d i n g Table XXXI which contains experimental d e t a i l s f o r i n d i v i d u a l runs. The s e n s i t i z e d photolysis of the enriched c i s pyrazoline ( c i s : trans r a t i o was 80:20) gave two peaks i n the v.p.c. (5% Carbowax-15% QF-1, 125°, 30 ml/min) of re t e n t i o n times 4.1 and 5.4 minutes. The peaks were i d e n t i f i e d by n.m.r. as trans- and cis- 1 , 2 - d i m e t h y l - l -a c e t y l cyclopropane (115) and (114) r e s p e c t i v e l y . The n.m.r. (60 MHz, CCl^, external TMS) i s that of the crude r e a c t i o n mixture with the s e n s i t i z i n g agent benzophenone present: 0.08 and 8.25 x ( s i n g l e t s ) a c e t y l methyls of the trans- and cis-cyclopropanes 115 and 114 r e s p e c t i v e l y , 10.00 x (multiplet) on of r i n g hydrogens. S i m i l a r l y , the s e n s i t i z e d photolysis of the enriched trans-pyrazoline 115 ( c i s : t r a n s r a t i o was 5:95) gave two peaks i n the v.p.c. of rete n t i o n times 4.3 and 6.1 minutes and were i d e n t i f i e d by n.m.r as the c i s - and trans-cyclopropanes 114 and 115 r e s p e c t i v e l y . The n.m.r. (60 MHz, CCl^, i n t e r n a l TMS) i s that of the crude r e a c t i o n mixture with benzophenone present: 7.94 x and 8.08 x (s i n g l e t s ) a c e t y l methyls of the cyclopropanes 114 and 115 r e s p e c t i v e l y . ~ 130 -(c) Distribution of products 1 Table XXVI. Distribution of Products from the Sensitized Photolysis of Pyrazolines 19^ and ^ 0 2 Pyrazolines 19:20 s.m< d.h.f. aB 3Y cis-A trans-A 80:20 0 0 0 0 64 36 5:95 0 0 0 0 54 46 100:03 0 0 0 0 67 31 0:1003 0 0 0 0 52 48 by at least 3 runs by v.p.c. ratio determined by n.m.r. integrals corrected to 100% using results of 80:^ 0_ and 5:95_ ratios 6. (3S*,4S*,5A*)- and (3S*14S*,5S*)-3,4-Dimethyl-3-acetyl-5-phenyl-1-pyrazolines (30) and (31) (a) Preparation of pyrazolines 0^_ and 31 The t i t l e compounds were prepared according to the procedure of McGreer (15). Addition of phenyldiazomethane (from 12 g (0.1 mole) of benzaldehyde hydrazone) to an ether solution of 9.8 g (0.1 mole) of 3-methyl-3-pentene-2-one gave after one week at room temperature 14.8 g of crude pyrazolines 30 and 31 i n a ratio of 63:37 as determined by n.m.r. - 131 -Column chromatography (Silica gel, ether-petroleum ether, 5:95 to 10:90) yielded a mixture of the pure pyrazolines. Two fractions in which the ratios of 30:31 were 69:31 and 62:38 were used for photolysis experiments. In order to increase the proportion of'31, advantage was taken of the fact that pyrazoline ^ 0_ decomposes much faster (about 9 times as fast, see Experimental § 11a ) as does pyrazoline 31. Thus by refluxing 6.9 g of the crude reaction mixture (the i n i t i a l ratio of 30:31 was 63:37)in acetone for 23 h followed twice by column chromato-graphy, a fraction weighing 590 mg was obtained in which the ratio of 30:31 was 5:95. This fraction was used for the photolysis experiments. For the pyrazoline 30: n.m.r. (100 MHz, CCl^) 7.61 and 8.82 x (singlets) acetyl and C-3 methyls respectively, 8.96 x (doublet J = 7,2 Hz) C-4 methyl, 5.37 x (doublet J = 10.8 Hz) C-5 hydrogen, 8.1 x (multiplet) C-4 hydrogen. For the pyrazoline 31: n.m.r. (100 MHz, CCl^) 7.77 and 8.53 x (singlets) acetyl and C-3 methyls respectively, 4.71 x (doublet J = 8c6 Hz) C_5 hydrogen, 7.30 x (quintet) C-4 hydrogen, 9.61 x (doublet J = 7.5 Hz) C-4 methyl. (b) Direct photolysis and product identification A general description of the experimental procedure is given in the Experiment § 9(a), including Table XXX which gives details of individual runs. The photolysis of pyrazolines 30^ and 31_ resulted in a slightly red coloured solution with the familiar odour of phenyl diazomethane. The v.p.c. (10% FFAP-10% DC 710, 165°, 50 ml/min) gave - 132 -a component at an i d e n t i c a l retention time as that of 3-methyl-3-pentene-2-one, (E)-(IOO). The n.m.r. of the crude reaction mixture gave two peaks i n the 7.82 T region, corresponding to the resonances expected f o r the a c e t y l methyls of the ketone E-100 and cyclopropane 37. I t should also be expected that 3-methyl-3-pentene-2-one, (Z)-(IOO) o be present since at 3500 A photochemical eq u i l i b r i u m between ketones E-100 and Z-100 i s established (see Experimental § 10a ) i n a r a t i o of 67:33. The percentage of the ketone present i n the crude re a c t i o n mixture was c a l c u l a t e d by comparison of i t s peak height i n the vapour phase chromatogram to the peak heights obtained from standardized s o l u t i o n s . There were four remaining peaks i n the v.p.c. (10% FFAP-10% DC 710, 205°, 120 ml/min) at higher column temperature and a higher flow ra t e , with retention times of 5.3, 6.0, 7.5 and 8.6 minutes. The 5.3 min component was i d e n t i f i e d on the basis of i t s v.p.c. r e t e n t i o n time as the cyclopropane 36_, and the other minor component of ret e n t i o n time 7.5 min was not i d e n t i f i e d . The 6.0 and 8.6 min components were i s o l a t e d by preparative v.p.c. and i d e n t i f i e d by n.m.r. as the cyclopropyl ketones 3_7 and 38. For the ketone _3_7: n.m.r. (100 MHz, CCl^) 7.77 T (quintet) C-3 hydrogen, 8.16 x (doublet J = 7.2 Hz) C-2 hydrogen, 8.34 and 8.56 x (si n g l e t s ) a c e t y l and C - l methyls r e s p e c t i v e l y , 8.77 x (doublet) C-3 methyl. For the ketone _38: n.m.r. (100 MHz, CCl^) 7.35 x (doublet J = 10.0 Hz) C-2 hydrogen, 7.88 and 7.92 x ( s i n g l e t s ) a c e t y l and C - l methyls respective, 8.24 x (multiplet) C-3 hydrogen, 8.97 x (doublet) C-3 methyl. - 1 3 3 -(c) S e n s i t i z e d photolysis and product i d e n t i f i c a t i o n A general d e s c r i p t i o n of the experimental procedure i s given i n the Experimental § 9(b) in c l u d i n g Table XXXI which gives d e t a i l s of i n d i v i d u a l runs. The v.p.c. ( 1 0 % FFAP - 1 0 % DC 7 1 0 ) showed four peaks with retention times of 5 . 3 , 6 . 0 , 7 . 5 and 8 . 6 minutes. The 5 . 3 and 8 . 6 min components were i d e n t i f i e d by t h e i r v.p.c. r e t e n t i o n times as the cyclopropanes 36_ and 3 8 . The 7 . 5 min component was not i d e n t i f i e d . The major product of retention time 6 . 0 min was i d e n t i f i e d by n.m.r. as the cyclopropane 3 6 . For the ketone _3JK n.m.r. ( 6 0 MHz, CCl^, i n t e r n a l TMS) 8 . 3 2 and 8 . 5 8 x (s i n g l e t s ) a c e t y l and C - l methyls r e s p e c t i v e l y , 7 . 8 x (multiplet) C - 3 hydrogen, 8 . 1 4 x (doublet J = 7 . 2 Hz) C - 2 hydrogen. (d) D i s t r i b u t i o n of products Table XXVII. Distribution"'' of Products from the Photolysis of Pyrazolines ^ 0 _ and 3 1 . 2 3 Conditions Ratio S t a r t i n g A A A 3 0 : 3 1 M a t e r i a l 3 6 3 7 un. 3 8 6 9 : 3 1 2 1 t r . 6 0 t r . 1 9 6 2 : 3 8 2 1 t r . 5 8 t r . 2 1 5 : 9 5 2 6 1 1 5 1 5 7 1 0 0 : 0 4 1 8 0 8 2 0 0 0 : 1 0 0 4 2 7 1 1 1 1 6 0 - 134 -hv-s 69:31 0 4 96 t r . 1 5:95 0. 6 90 1 3 100:0 4 0 2 98 t r . 0 0:100 4 0 6 90 1 3 by at l e a s t 3 runs by v.p.c. 2 as determined by n.m.r. 3 3-methyl-3-pentene-2-one, (E)-(100) 4 corrected to 100% using r e s u l t s of 69:31 and 5:95 r a t i o s . 7. (3S*,4R*,5R*)- and (3S*,4R*,5S*)-3,4-Dimethyl-3-acetyl-5-phenyl-1-pyrazoline (32) and (33) (a) Preparation of pyrazolines 22_ and 33 The t i t l e compounds were prepared according to the procedure of McGreer (15). Addition of phenyl diazomethane (prepared from 2.4 g (0.11 mole) of benzaldehyde hydrazone) to an ether s o l u t i o n of 0.90 g (0.90 mole) of e-methyl-3-pentene-2-one, (Z)-(100) gave 2.4 g of crude pyrazoline _32_ and J3_3. Column chromatography ( s i l i c a g e l , ether-petroleum ether, 4:96 to 10:90) y i e l d e d a f r a c t i o n weighing 743 mg of white c r y s t a l s . R e c r y s t a l l i z a t i o n from ether-petroleum ether (10:90) gave white c r y s t a l s of the pyrazolines 32_ and _33 i n a r a t i o of 40:60. Further r e c r y s t a l l i z a t i o n y i e l d e d more white c r y s t a l s i n which the r a t i o of j32_ and 33_ was 80:20. The two batches of c r y s t a l s were used for the photolysis experiments. For the pyrazoline 32_: n.m.r. (100 MHz, CCl^) 7.98 and 8.42 T ( s i n g l e t s ) a c e t y l and C-3 methyls r e s p e c t i v e l y , 5.16 T (doublet J = 9.6 Hz) C-5 hydrogen, 9.02 T (doublet J = 6.8 Hz) C-4 methyl, 8.4 to - 135 -8.6 T (multiplet)C-4 hydrogen. For the p/razoline 33.: n.m.r. (60 MHz, CCl^) 7.57 and 8.70 x (s i n g l e t s ) a c e t y l and C - l methyls r e s p e c t i v e l y , 4.70 x (doublet J = 7.2 Hz) C-5 hydrogen, 9.80 x (doublet J = 7.2 Hz) C-4 methyl, 7.7 x region (multiplet) C-4 hydrogen. (b) Di r e c t photolysis and product i d e n t i f i c a t i o n A general d e s c r i p t i o n of the experimental procedure i s given i n the Experimental § 9(a), i n c l u d i n g Table XXX which gives d e t a i l s of i n d i v i d u a l runs. There were three peaks i n the v.p.c. (10% FFAP-10% DC 710, 205°, 120 ml/min) with retention times of 5.3, 6.0 and 8.6 minutes. The 6.0 and 8.6 min components were i d e n t i f i e d on the basis of t h e i r v.p.c. retention times. The 5.3 min component was i s o l a t e d by preparative v.p.c. and i d e n t i f i e d by n.m.r. as the cycloprop ane 36. For the cyclopropane 36: n.m.r. (100 MHz, CCl^) 7.84 and 8.95 x (s i n g l e t s ) a c e t y l and C - l methyls r e s p e c t i v e l y , 7.18 x (doublet J = 6.8 Hz) C-2 hydrogen, 8.4-8.7 x region (multiplet) C-3 hydrogen, 8.88 x (doublet J = 6.2 Hz) C-3 methyl. (c) S e n s i t i z e d photolysis and product i d e n t i f i c a t i o n The general procedure i s given i n the Experimental § 9(b) inc l u d i n g Table XXI which gives d e t a i l s of i n d i v i d u a l runs. The v.p.c. (10% FFAP-10% DC 710, 205°, 120 ml/min) gave three peaks i n the v.p.c. with retention times of 5.3, 6.0 and 8.6 minutes. A l l components were i d e n t i f i e d on the basis of t h e i r v.p.c. retention times as the cyclopropanes _36_, 37 and 38. - 136 -(d) D i s t r i b u t i o n of products Table XXVIII. D i s t r i b u t i o n of Products from the Photolysis of Pyazolines 31_ and 33_ _ Conditions Ratio A A A 32:3.3 36 37 38 hv-d 80:20 97 3 t r . 40:60 98 2 t r . 100:0 3 96 4 t r . 0:100 3 99 1 t r . hv-s 80:20 95 4 1 40:60 97 3 t r . 100:0 3 94 5 1 0:100 3 99 1 t r . by at l e a s t three runs by v.p.c. 2 as determined by v.p.c. 3 corrected to 100% using r e s u l t s of 80:20 and 40:60 r a t i o s 8. (3S*,4S*,5S*)- and (3S*,4S*,5R*)-3,5-dimethyl-3-acetyl-4-phenyl-1-pyrazolines (34) and (35) (a) Preparation of pyrazolines j34_ and 35_ The t i t l e compounds were prepared according to the procedure of McGreer (15). Three successive treatments of 16.0 g (0.1 mole) of 4-phenyl-3-butene-2-one with diazoethane (from 33.0 g (0.28 mole) of N-nitroso-N-ethyl urea) gave the crude pyrazolines 34:35 i n a r a t i o of - 137 -9:1. The major product 3^4 was c r y s t a l l i z e d out of s o l u t i o n leaving the mother l i q u o r with a 50:50 r a t i o of 34:35. Further p u r i f i c a t i o n by column chromatography gave the pure pyrazolines 3^4_:3_5 i n a r a t i o of 45:55. This f r a c t i o n together with pure r e c r y s t a l l i z e d _35_ were us i n the photoly s i s experiments. For the pyrazoline 34_: n.m.r. (60 MHz, CCl^) 7.61 and 9.01 x (si n g l e t s ) a c e t y l and C-3 methyls r e s p e c t i v e l y , 5.31 x (quintet) C-5 methyl, 6.86 x (doublet J = 8.2 Hz) C-4 hydrogen. f o r the pyrazoline 35: n.m.r. (100 MHz, CCl^) 7.83 and 8.58 x (s i n g l e t s ) a c e t y l and C-3 methyls r e s p e c t i v e l y , 5.98 x (quintet) C-5 hydrogen, 6.34 x (doublet J = 7.0 Hz). (b) D i r e c t photolysis and product i d e n t i f i c a t i o n The general procedure i s given i n the Experimental § 9(a) in c l u d i n g Table XXX which gives d e t a i l s of i n d i v i d u a l runs. The v.p.c. (20% FFAP, 210°, 120 ml/min) gave f i v e peaks with r e t e n t i o n times of 6.0, 6.7, 7.1, 10.4 and 11.4 minutes. For the photoly s i s of 100% 3k_ the 6.0 min component was i d e n t i f i e d by v.p.c. retention time as the a,$- and 8,y-ketones 125 and 126. The 7.1 and 11.4 min components were i d e n t i f i e d also by v.p.c. r e t e n t i o n times as the cyclopropyl ketones _37_ and 3_8 re s p e c t i v e l y . The 10.4 min component was not i d e n t i f i e d . The 6.7 min component was i d e n t i f i e d by n.m.r. as the cyclopropyl ketone 36_. For the ketone 36_: n.m.r. (60 MHz, CCl^) 7.79 and 8.90 x (si n g l e t s ) a c e t y l and C - l methyls r e s p e c t i v e l y , 7.15 x (doublet J = 6.8 Hz). - 138 -For the photolysis of the mixture of _34_ and 3_5 the 6.0 min component was i d e n t i f i e d by i t s retention time as the ketones 125 and 126. The 7.1 min component was i d e n t i f i e d by i t s v.p.c. r e t e n t i o n time as the cyclopropyl ketone 37. The 6.7 min component was i s o l a t e d by preparative v.p.c. containing the 6.0 min peak plus a considerable amount of the y,6— ketones a r i s i n g from thermal rearrangement of 3>6_ on the v.p.c. column. The 6.7 min peak was thus i d e n t i f i e d by n.m.r. as the cyclopropyl ketone 3 6 : n.m.r. (100 MHz, CCl^) 7.84 and 8.95 x ( s i n g l e t s ) a c e t y l and C - l methyls, 7.17 x (doublet J = 6.8 Hz) C-2 hydrogen, 8.86 x (doublet) C-3 methyl. The spectrum also included several smaller peaks presumably due to the a,8- and B,y-ketones 125 and 126. The 11.4 min component was i s o l a t e d by preparative v.p.c. and i d e n t i f i e d by n.m.r. as the cyclopropyl ketone 38: n.m.r. (100 MHz, CCl^) 7.86 and 8.90 x (s i n g l e t s ) a c e t y l and C - l methyls r e s p e c t i v e l y , 7.31 x (doublet J = 9.8 Hz) C-2 hydrogen, 8.23 x (multiplet) C-3 hydrogen, 8.96 x (doublet) C-3 methyl. (c) Sen s i t i z e d photolysis and product i d e n t i f i c a t i o n A general d e s c r i p t i o n of the experimental procedure i s given i n the Experimental § 9(b) incl u d i n g Table XXXI which gives d e t a i l s of i n d i v i d u a l runs. The v.p.c. (20% FFAP, 210°, 120 ml/min) gave four peaks with retention times 6.0, 6.7, 7.1, and 11.4 minutes. The 6.0 min component was present i n only a trace amount and was i d e n t i f i e d by i t s v.p.c. retention time as the a,8- and B,y-ketones 125 and 126. The 7.1 and 11.4 min components were not i s o l a t e d and - 139 -were i d e n t i f i e d on the basis of t h e i r v.p.c. r e t e n t i o n times as the cyclopropyl ketones J7 and 38. The 6.7 min component was i d e n t i f i e d by n.m.r. as the cyclopropyl ketone _36: n.m.r. (60 MHz, CCl^, i n t e r n a l TMS) 7.82 and 8.95 x (si n g l e t s ) a c e t y l and C - l methyls r e s p e c t i v e l y , 7.14 T (doublet J = 6.8 Hz) C-2 hydrogen. (d) D i s t r i b u t i o n of products Table XXIX. D i s t r i b u t i o n 1 of Products from the Photolysis of Pyrazolines 34 and 35 Conditions „ • 2 Ratio 34:35 3 Ol e f i n s 36 37 un. 38 hv-d 100:0 1 95 2 0 2 45:55 14 57 1 1 27 0:100 4 25 26 0 0 47 hv-s 100:0 t r . 96 2 2 2 45:55 t r . 96 2 2 2 0:100 4 t r . 96 2 2 2 by at l e a s t three runs by v.p.c. as determined by v.p.c. a mixture of 125 and 126 corrected to 100% using 100:0 and 45:55 r a t i o s - 140 -9. Photolysis of Pyrazolines (a) Method for d i r e c t photolysis The pyrazolines i n t h i s work were photolyzed as .0040 to .0188 molar solutions i n d i e t h y l ether (Mallinckrodt) f o r 0.5 to 2.75 h at o 3500 A (Rayonet Reactor) using a pyrex re a c t i o n v e s s e l . The ether was then removed by rotatory evaporation and the crude r e a c t i o n mixture was examined by v.p.c. to determine the d i s t r i b u t i o n of products. Table XXX gives d e t a i l s of the i n d i v i d u a l experiments. Table XXX. Experimental Conditions for the Di r e c t Photolysis of Pyrazolines Pyrazoline Pyrazoline (mg) Solvent (ml) Pyrazoline ^ (molarity x 10 ) Time (h) cis-98 200 100 14.3 2.0 II 75 40 13.4 1.1 II 105 80 9.3 1.5 II 100 80 8.9 5.0 trans-99 100 50 14.3 2.75 II 200 80 17.8 1.75 30:31 (62:38) 100 100 4.6 0.5 (69:31) 30 25 5.6 0.5 ( 5:95) 95 100 4.4 0.5 32:33 (80:20) 98 100 4.5 0.5 (40:60) 90 100 4.0 0.5 33:34 (100:0) 110 100 5.1 0.5 ( 45:55) 110 100 5.1 0.5 - 141 -(b) Method for s e n s i t i z e d photolysis The pyrazolines 19, 20, 98. a n d 99 photolyzed as .0089 to .0166 molar solutions i n n-pentane (Fisher, p e s t i c i d e grade) for 0.7 to 1.0 h o at 3500 A (Rayonet Reactor) using a pyrex r e a c t i o n v e s s e l . Benzophenone (BDH, reagent) i n a molar excess ranging from 10.4 to 25.6 was used as the s e n s i t i z e r . The re a c t i o n v e s s e l was flushed with a stream of oxygen free nitrogen p r i o r to and during the p h o t o l y s i s . The n-pentane was then removed by rotatory evaporation and the crude r e a c t i o n mixture was dissolved i n a minimum amount of ether. This mixture was then examined by v.p.c. to determine the d i s t r i b u t i o n of products. A f t e r three or four i n j e c t i o n s the column temperature was r a i s e d to elute the benzophenone. The remaining pyrazolines 3_0_ to 15 were photolyzed as .0041 to .0069 molar s o l u t i o n f o r 0.5 to 1.0 h using s i m i l a r conditions. Benzophenone was used i n a 16.2 to 28.2 molar excess. In order to analyze the product d i s t r i b u t i o n s by v.p.c. i t was e s s e n t i a l to f i r s t of a l l reduce the r a t i o of the molar concentration of products: benzophenone to about 1:1 by a bulb to bulb d i s t i l l a t i o n . The d i s t i l l a t e was then examined by v.p.c. to obtain the product d i s t r i -butions. A f t e r the products were eluted the column temperature was then r a i s e d a f t e r each i n j e c t i o n to remove the benzophenone. Table XXXI contains d e t a i l s of i n d i v i d u a l experiments. - 142 -Table XXXI. Experimental Conditions f o r the S e n s i t i z e d Photolysis of Pyrazolines. Pyrazoline Pyrazoline (mg) Solvent (ml) Pyrazoline (molarity x 103) Benzo-phenone (g) Mole 1 r a t i o Time (h) cis-98 140 60 16.6 2.00 10.4 1.0 30 20 10.5 1.00 25.6 1.0 trans-99 140 60 16.6 1.97 10.8 1.0 45 20 16.1 1.00 17.1 1.0 cis-19 70 30 16.6 1.82 20.0 0.7 trans-20 25 20 8.9 0.32 9.8 0.7 25 20 8.9 0.49 15.1 0.7 25 20 8.9 0.68 20.9 0.7 30:31 (69:31) 120 80 6.9 1.85 18.2 0.6 (69:31) 83 60 6.4 1.2 17.2 1.0 ( 5:95) 42 45 4.3 0.67 16.9 0.6 32:33 (80:20) 22 25 4.1 0.30 16.2 0.6 (40:60) 25 20 5.8 0.42 16.8 0.6 34:35 (100:0) 103 80 5.9 1.46 28.2 0.5 ( 45:55) 80 60 6.1 1.30 19.3 0.6 mole r a t i o r e f e r s to that of benzophenone/pyrazoline. - 143 -10. Control Experiments (a) Direct photolysis Control experiments were done under s i m i l a r conditions as the d i r e c t photolysis of the pyrazolines. The compounds examined were o thus photolyzed at 3500 A (Rayonet Reactor) i n ether using a pyrex r e a c t i o n v e s s e l . The crude re a c t i o n mixtures were examined by v.p.c. at various time i n t e r v a l s . The conditions of i n d i v i d u a l c o n t r o l experiments are given i n Table XXXII Table XXXII. Experimental Data f o r Di r e c t Photolysis Control Experiments Compound Weight Ether Concentration Time (mg) (ml) (molarity x 10 3) (h) cls-114 20 20 8.9 1.0 2.0 3.0 5.0 trans-115 20 20 8.9 0.5 1.0 2.0 E-100 40 40 10.2 1.5 2.5 36 24 25 5.1 0.5 1.0 1.75 1L 25 25 5.3 1.0 2.0 3.0 38 21 20 5.6 1.0 2.0 3.0 - 144 -In a l l runs except that of the ketone 100 the compounds i n question d i d not undergo rearrangement. In the case of 3-methyl-3-pentene-2-one, (E)-(100), i t was found that a photostationary e q u i l i b r i u m was established with the corresponding Z-100 isomer i n a r a t i o of 2:1 i n favour of the E_ isomer. (b) S e n s i t i z e d p h o t o l y s i s Control experiments were done under s i m i l a r conditions as the s e n s i t i z e d p h o t o l y s i s of the pyrazolines. The compounds examined o were thus photolyzed i n n-pentane at 3500 A (Rayonet Reactor) i n a pyrex reaction v e s s e l . Benzophenone was used as the s e n s i t i z e r . The crude reaction mixtures were examined e i t h e r by v.p.c. or n.m.r. or a combination of both at various time i n t e r v a l s . The conditions used f o r i n d i v i d u a l c o n t r o l experiments are given i n Table XXXIII. A l l the cyclopropyl ketones were found not to undergo c i s - t r a n s isomerization, conversion to a dihydrofuran, or s t r u c t u r a l rearrangement to a,$- and B,y-unsaturated ketones, nor to y,6-unsaturated ketones. A c o n t r o l run was done on a blank sample using only n-pentane and benzophenone. A f t e r photolysis the n-pentane was removed by rotatory evaporation and an n.m.r. was run on the residue. Several absorptions were noted between 8.2 to 9.4 x with a sharp s i n g l e t at 6.2 x which underwent deuterium exchange as evidenced by n.m.r. - 145 -Table XXXIII. Experimental Data f o r S e n s i t i z e d Photolysis Control Experiments Compound Weight (mg) n-Pentane (ml) Cyclopropane (molarity x 10 3) Benzo-phenone (mg) Mole 1 Ratio Time (h) cis-114 32 25 11.4 518 10.0 1.0 32 25 11.4 518 10.0 2.0 trans-115 25 20 11.2 324 8.0 1.1 25 20 11.2 324 8.0 4.5 36 30 30 5.3 475 16.4 0.5 37 72 60 6.4 1209 17.3 1.0 38 75 60 6.6 1000 13.8 0.5 2.0 n-pentane - 40 - 690 - 1.0 - 40 - 690 - 2.0 Mole r a t i o r e f e r s to that of benzophenone/pyrazoline. 11. Relative Rates f o r the Thermal Decomposition of Pyrazolines (a) Relative Rates of Pyrazolines j30_ and 31 Run 1 - To 50 ml of acetone was added 32 uJ, of a n i s o l e . The mixture was refluxed (56.5°) and 1.20 g of the crude pyrazolines ^0 and ( s t a r t i n g r a t i o was 63:37) were aded and a 5 ml a l i q u o t was immediately removed. At s p e c i f i c time i n t e r v a l s a d d i t i o n a l 5 ml al i q u o t s were taken. A f t e r each sample was removed, the acetone was removed by rotatory evaporation and a n.m.r. spectrum i n CCl^ was obtained i n the 4 to 7 T region. In t h i s region three resonances were observed: (1) 4.65 x (doublet J = 8.5 Hz) C-5 hydrogen of - 146 -pyrazoline 2, (2) 5.32 T (doublet J = 10.8 Hz) C-5 hydrogen of pyrazoline 1_, and (3) 4.32 x ( s i n g l e t ) methyl of a n i s o l e . The n.m.r. spectra i n which anisole was used as a standard i n t e r n a l i n t e g r a l allowed the decomposition of the pyrazolines to be monitored and a rate constant to be c a l c u l a t e d . Run 2 - In a s i m i l a r manner 2.25 g of the crude pyrazolines J30_ and _31^  ( s t a r t i n g r a t i o was 63:37) were decomposed i n r e f l u x i n g acetone i n which 30 y£ of anisole had been added. Run 1 was used to follow the rate of decomposition of pyrazoline 30; whereas, Run 2 was used to determine the rate of decomposition of pyrazoline 31. Results are recorded i n Table XXXIV. Table XXXIV. Relative Rates of Decomposition of Pyrazolines 30_ and 31 Run Time Ratio of % Decomp. % Decomp. (h) 30:31 of 31 of 30 0 73:126 0 -3.0 59:72 43 -4.5 55:50 60 -6.0 56:45 64 -7.5 55:34 73 -9.0 54:20 79 -0 90:154 - 0 12 67:- - 25 24 53: - 41 36 44: - 51 48 40: - 56 60 35: _ 61 147 -From the data i n Table XXXIV - run 1, the f i r s t order rate constant was c a l c u l a t e d f o r the decomposition of pyrazoline 31. S i m i l a r l y thecata i n Table XXXIV - run 2, allows c a l c u l a t i o n of the f i r s t order rate constant k„ f o r pyrazoline 30. (b) R e l a t i v e rates of pyrazolines _3_2_ and 3^3 P u r i f i c a t i o n of the pyrazolines 32_ and _3J3_ by column chromatography gave 496 mg i n a r a t i o of 7:3. A f t e r several weeks at room temperature a second p u r i f i c a t i o n by column chromatography gave 216 mg of the pyrazolines 32^ and ^3 i n a r a t i o of 1:1. These figures permitted the c a l c u l a t i o n of the r a t i o of the r e l a t i v e rates of decomposition of pyrazoline 32/pyrazoline 33 as approximately 4/1. (c) R e l a t i v e rates of pyrazolines 34_ and 35 To 25 ml of toluene was added 18 u£ of 1,1-diphenyl ethylene. The mixture was refluxed (111°) and 150 mg of p u r i f i e d pyrazolines 34 and 35^ ( s t a r t i n g r a t i o was 34:66) were added and a 5 ml a l i q u o t was immediately taken. At s p e c i f i c time i n t e r v a l s a d d i t i o n a l 5 ml aliquots were removed. A f t e r each sample was removed, the toluene was removed and an n.m.r. spectrum was obtained i n the 4 to 7 T region. I n i t i a l l y t h i s region showed f i v e resonances: 4.68 x ( s i n g l e t ) v i n y l protons of diphenyl ethylene, 5.27 and 5.95 x (quintets) C-5 hydrogens of pyrazolines 3_4_ and 35_ r e s p e c t i v e l y , 6.33 and 6.85 x (doublets) C-4 = 7.5 x 10 = 8.5 x 10 = 9 - 148 -hydrogens of pyrazolines 85 and J34_ r e s p e c t i v e l y . The n.m.r. spectra of the al i q u o t s indicated that the pyrazoline 35 decomposed much f a s t e r than the pyrazoline 34. Aft e r 0.8 h 122! was 12% decomposed; a f t e r 1.5 h, 29%; and a f t e r 2.0 h, 35%. However, 15 appeared to be t o t a l l y decomposed a f t e r 0.8 h. The r e l a t i v e rates of 34/35 i s therefore le s s than 0.1. 12. Nuclear Overhauser E f f e c t s (a) General experimental procedure Compounds to be studied were dissolved i n CCl^ and f i l t e r e d through f i n e s i n t e r e d glass i n t o n.m.r. tubes f i t t e d with an extension that had a r e s t r i c t i o n . This was followed by degassing using four freeze-pump-thaw c y c l e s . Concentrations of the compounds studied va r i e d from approximately 0.2 to 0.3 molar. E i t h e r hexamethyldisiloxane or 1,1,2,2-tetrachloroethane was used as the i n t e r n a l lock. A concentration of the i n t e r n a l i n t e g r a l standard, p-dioxane, was used such that i t s area upon i n t e g r a t i o n was approximately equal to the area of the resonances observed. Spectra were recorded on a Varian Associates HA-100 spectrometer using a frequency sweep mode. The second r . f . f i e l d YL was obtained by using a Hewlett Packard Model 204B audio generator with a 465 A am p l i f i e r . The Overhauser enhancements were measured by f i r s t recording the areas of the protons to be observed r e l a t i v e to the area of the i n t e r n a l i n t e g r a l . Second, the i r r a d i a t i n g f i e l d was positioned at the required frequency and power to saturate the protons i n question and then the areas of the observed protons plus the i n t e r n a l - 149 -i n t e g r a l standard were recorded. The percent enhancements are calc u l a t e d as the increase i n area r e l a t i v e to the i n t e r n a l i n t e g r a l standard for both i r r a d i a t i n g and n o n - i r r a d i a t i n g conditions. I r r a d i a t i o n s were c a r r i e d out at varying power l e v e l s i n order to optimize the enhancements. At l e a s t three i n t e g r a t i o n s were performed under both i r r a d i a t i n g conditions and n o n - i r r a d i a t i n g conditions. (b) Preparation of the pyrazoline _34_ and the dihydrofuran j?6_ f o r N . O . E . studies The preparation of the pyrazoline 34_ was according to the procedure given i n the Experimental § 8.1. P u r i f i c a t i o n was accomplished by r e c r y s t a l l i z a t i o n from etherrpetroleum ether ( 1 0 : 9 0 ) . The dihydrofuran 96_ was prepared by i r r a d i a t i o n of 150 mg of the o cyclopropyl ketone _36_ i n 120 ml of ether at 3100 A (Rayonet Reactor) f o r 1 day. The ether was removed by rotatory evaporation followed by v.p.c. ( 1 0 % FFAP-10% DC 7 1 0 , 2 0 5 ° , 60 ml/min). The c o l l e c t e d sample was immediately dissolved i n CCl^ and prepared f o r N . O . E . studies. The f i r s t N . O . E . experiment for the pyrazoline was set up i n order to successively i r r a d i a t e the C-3 and C-5 methyls and to observe the enhancement of the C-4 and C-5 hydrogens. To 1.0 ml of -4 CCl^ was added 60 mg ( 2 . 7 8 x 10 mole) of the pyrazoline 34., 3.4 mg -4 ( 0 . 3 9 x 10 mole) of p-dioxane (the i n t e r n a l i n t e g r a l standard), and 150 u£ of sym-tetrachloroethane (the i n t e r n a l l o c k ) . The second N . O . E . experiment for the pyrazoline J34_ allowed f o r the i r r a d i a t i o n of the C-5 phenyl group and the observation of the - 150 -enhancements of the C-4 and C-5 hydrogens. To 800 u£ of CCl^ was -4 added 40 mg (1.85 x 10 mole) of the pyrazoline _34_, 4.7 mg (0.53 x 10 mole) of p-dioxane (the i n t e r n a l i n t e g r a l standard), and about 30 y£ of tetramethyldisiloxane (the i n t e r n a l l o c k ) . The t h i r d N.O.E. experiment f o r the dihydrofuran 96_ allowed f o r the i r r a d i a t i o n of the C-4 methyl group and the observation of the enhancement of the C-2 and C-3 hydrogens. To 1.0 ml of CCl^ was added -4 -4 36 mg (1.91 x 10 mole) of the dihydrofuran 96, 2.2 mg (0.25 x 10 mole) of p-dioxane (the i n t e r n a l i n t e g r a l standard) and 50 u£ of sym-tetrachloroethane (the i n t e r n a l l o c k ) . (c) N.O.E. r e s u l t s The r e s u l t s are recorded i n Table I I I of the Results. 13. Rearrangement of Tetrasubstituted Cyclopropanes (a) Experimental conditions The thermal experiments were accomplished by using degassed samples of the appropriate cyclopropyl ketone (2.2 mg) i n pyrex tubing (4.2 mm i . d . x 100 mm). In a s i m i l a r manner photochemical runs were done by using degassed samples of the cyclopropyl ketone (2.2 mg) i n pyrex tubing (4.2 mm i . d . x 50 mm). Samples were photolyzed at o 3.00 A i n a Rayonet Reactor. The progress of the reac t i o n was monitored by a P.E. 226 a n a l y t i c a l v.p.c. using a Carbowax 20-m (.01 i . e . x 150') at 175° with a head pressure of 18 p . s . i . - 151 -(b) I d e n t i f i c a t i o n of dihydrof urans 96_ and 97_ Large scale preparation of the dihydrofuran 96_ was accomplished by heating s e v e r a l 12 mg samples of the cyclopropyl ketone _36_ i n 920 u£ reac t i o n vessels at 338° for 10 minutes. The v.p.c. showed one major peak (20% FFAP, 205°, 120 ml/min) with a 7.0 min retention time. This r e t e n t i o n time was considerably l e s s than any of the cyclopropyl ketones _36_, 27_ or J38 or any of the isomeric a,B-, B,y- or y-& unsaturated ketones. This major peak was i s o l a t e d by preparative v.p.c. as a clear colourless l i q u i d . I t was i d e n t i f i e d on the basis of i t s i . r . , u.v. and n.m.r. spectra as 3,4,5-trimethyl-5-phenyl-trans-4,5-dihydrofuran (96)• For the dihydrofuran 96_: i . r . 1700 cm \ double bond of enol ether; u.v. (EtOH) end absorption only; n.m.r. (60 MHz, CCl^) 8.46 T and 8.22 x ( s i n g l e t s showing long range coupling ) C-4 and C-5 methyls, 8.94 x (doublet J = 7.0 Hz) C-3 methyl, 7.03 x (multiplet) C-3 hydrogen, 5.18 x (doublet J = 8.0 Hz) C-2 hydrogen. Anal. Calcd. f o r C._H,,0: C, 82.93; H, 8.57. Found: C, 82.74; ± 3 l b H, 8.34. In a d d i t i o n , 100 mg of the cyclopropyl ketone 36_ i n 100 ml of o ether was photolyzed f o r 24 h at 3100 A (Rayonet Reactor). The v.p.c. showed one major component (65%) with a retention i d e n t i c a l to the dihydrofuran 96^  i s o l a t e d by the thermolysis of the cyclopropyl ketone 36. The product i s o l a t e d by preparative v.p.c. gave a s i m i l a r pattern i n n.m.r. spectrum: (60 MHz, CCl^) 8.36 and 8.50 x ( s i n g l e t s f o r the C-4 and C-5 methyls, 8.90 x (doublet) C-3 methyl, 7.5 x (multi-p l e t s ) C-3 hydrogen, 5.32 x (doublet) C-2 hydrogen. - 152 -The dihydrofuran i s o l a t e d from the above two reactions was found to be extremely s e n s i t i v e on exposure to the atmosphere, presumably to the water content (76 ). On leaving neat 96_ exposed to the a i r for as l i t t l e as 10 min, white c r y s t a l s began to appear. A f t e r one week the c r y s t a l s were r e c r y s t a l l i z e d from ether:petroleum ether (10:90). For the water adduct: the n.m.r. (60 MHz, CCl^.u c e l l ) displayed a broad absorption at 2.7 x for the aromatic hydrogens, a s e r i e s of peaks (IH) at 5.5 x, another s e r i e s (IH) from 6.6 to 7.3 x, and several absorptions (about 11H) from 7.8 to 9.3 x. Anal. Calcd. f o r C 1 0H 1 00_: C, 75.69; H, 8.80. Found: C, 74.66; H, 8.56. A corre c t a n a l y s i s corresponding to the water adduct could not be obtained. Presented i s the average of three analyses. The actual structure of the product r e s u l t i n g from exposure of the dihydrofuran to a i r i s not of prime importance. What i s of most importance i s that precautions be made to avoid such a re a c t i o n since pure samples of the dihydrofuran 96_ were required f o r c o n t r o l runs under thermal and p h o t o l y t i c conditions and for nuclear Overhauser experiments. A nuclear Overhauser e f f e c t was performed on the dihydrofuran 96. The experimental procedure i s given i n Section 12(a) of the Experimental. Discussion of the r e s u l t s are contained i n Section 4(a) of the Results. In b r i e f , the C-4 methyl group was i r r a d i a t e d and an enhancement of 23% was observed i n the C-5 hydrogen. This confirms the trans r e l a t i o n s h i p of the C-4 and C-5 hydrogens. - 153 -Si m i l a r large scale preparations were c a r r i e d out on the c y c l o -propyl ketone 38^  as were c a r r i e d out on the cyclopropyl ketone 36. A product of s i m i l a r r e t e ntion time to that of the dihydrofuran 96 was i s o l a t e d by v.p.c. (20% FFAP, 200°, 120 ml/min). The n.m.r. in d i c a t e d that two compounds were present i n about a 4 : 1 r a t i o with the major product being the previously i s o l a t e d dihydrofuran 96. The minor component was i d e n t i f i e d by n.m.r. as the isomeric 3 , 4 ,5-trimethyl-5-phenyl-cis-dihydrofuran (97). The two absorptions i n the n.m.r. (60 MHz, CCl^) of i n t e r e s t were two doublets, one at 4.62 T (J = 9 . 2 Hz) f o r the C-5 hydrogen and the other at 9.50 x (J = 7 .2 Hz) for the C -4 methyl. No other resonances of the dihydro-furan 97_ could be c l e a r l y designated. (c) Thermal and photochemical r e s u l t s The thermal r e s u l t s f o r the cyclopropyl ketones j36_, J37_ and J38 are presented i n Tables X, XI, and XII r e s p e c t i v e l y i n Section 4(b) of the Results. The photochemical r e s u l t s are contained w i t h i n Tables XIII, XIV and XV r e s p e c t i v e l y of the same se c t i o n as above. (d) Control runs Since the r a t i o of the two dihydrofuran products 96_ and 9_7 i s c r u c i a l , i t i s necessary to test for the p o s s i b i l i t y of t h e i r interconversion under both thermal and p h o t o l y t i c conditions. Degassed samples (2 .2 mg) of a mixture of the dihydrof urans 9_6 and 97_ i n pyrex tubing (4 .2 mm i . d . x 100 mm) were heated at 2 8 4 . 2 ° Q f o r a v a r i e t y of time i n t e r v a l s . The r a t i o of 96_ and _9_7. remained - 154 -constant throughout. Only a f t e r 15.5 h did there appear i n the vapour phase chromatogram several trace peaks (< 1% of t o t a l ) , three of which had s i m i l a r retention times to the cyclopropyl ketone _36_ and the y»6-unsaturated ketones 123 and 124. The photochemical c o n t r o l runs on the dihydrof urans 96_ and 97_ were done on degassed samples (2.2 mg) i n pyrex tubing (4.2 mm i . d . x o 100 mm) that were photolyzed at 3100 A for a v a r i e t y of time i n t e r v a l s . The r a t i o of 96;97 remained constant throughout. A f t e r 15.5 h two trace peaks appeared i n the chromatogram, t h e i r r e t e n t i o n times being s i m i l a r to the cyclopropyl ketones J36_ and 37. Table XXXV. Experimental Data f o r Thermal and Photochemical S t a b i l i t y of Dihydrofurans 96_ and 97_ Ratio 96:97 Time (h) Conditions (°C or A) Ratio 96:97 Time (h) Conditions (°C or A) 96:4 0.1 285.0 83:17 19.0 295.0 96:4 2.0 284.2 96:4 4.0 3100 96:4 4.0 284.2 96:4 8.0 3100 96:4 15.5 284.2 96:4 15.5 3100 83:17 6.0 284.2 83:17 4.0 3100 83:17 15.7 295.0 83:17 15.5 3100 Since the proportion of the dihydrofurans 96_ and 97_ to the y unsaturated ketones 123 and 124 changes r a p i d l y over a temperature range of l e s s than 100°, i t i s necessary to check that the r a t i o obtained - 155 -by v.p.c. analysis r e f l e c t s the true r a t i o . This check was necessary only f o r preliminary runs using an Aerograph Model A-90-P v.p.c. equipped with a thermal conductivity detector. Known r a t i o s of the dihydrofurans 96_ and 97; y, 6 - o l e f i n s 123 and 124 were found to integrate w i t h i n experimental e r r o r . It was found that the r a t i o of the dihydrof urans 96_ and 97; y,6-unsaturated ketones. 123 and 124 (designated D.H.F.: y,6) changed considerably depending on the time of r e a c t i o n , see Table X of the Results. I t was therefore necessary to check on the thermal s t a b i l i t y of these compounds. The following c o n t r o l i s s i m i l a r to that reported i n Table XXXV except i n t h i s case the mass balance of the re a c t i o n was measured by constant volume i n j e c t i o n using an Aerograph A-90-P v.p.c. and a Honeywell Model E l e c t r o n i c 15 recorder equipped with a d i s c chart i n t e g r a t o r . Four degassed 3.8 mg samples of the dihydrofurans 96 and 97_ i n 720 u£ re a c t i o n vessels were thermolyzed at 338° f o r times of 5, 10, 15, and 20 min, a f t e r which the mass balance decreased to 98, 93, 91 and 85% r e s p e c t i v e l y . Only trace amounts of other peaks were present i n the chromatogram. Similar experiments were c a r r i e d out on the y^-ketones 123 and 124. Five degassed 3.8 mg samples of a mixture of the ketones 123 and 124 were heated at 338° i n 720 u£, re a c t i o n vessels f o r 5, 10, 15, 30, and 95 min. The mass balance decreased sharply with accompanying charring. A new peak on the v.p.c. (20% FFAP, 205°, 120 ml/min) appeared at a very long retention time of 24.0 min. This new peak reached a maximum y i e l d of 25% and has yet to be i d e n t i f i e d . - 156 -In addition to the above two experiments, a known D.H.F.: y,6-r a t i o of 45:55 (3.0 u£ samples) heated at 313°C i n degassed pyrex tubes (4.2 i . d . x 100 mm) f o r a v a r i e t y of times ranging from 10 tO 50 min. As time progressed the i n i t i a l D.H.F.: y,& r a t i o of 45:55 reduced gradually to 63:37 while at the same time the mass balance reduced to l e s s than 50%. This r e s u l t i n d i c a t e s that the y,&-ketones 123 and 124 disappear, presumably by polymerization, f a s t e r than the dihydrofurans 9_6_ and 9_7 do. The change i n r a t i o D.H.F.: y,6 i s not due to any interconversion of the dihydrofurans with the y,6-unsaturated ketones. 14. K i n e t i c Studies (a) Experimental conditions A mixture (3.0 to 3.5 mg) of the cyclopropyl ketones 132 and 133 i n degassed pyrex tubing (4.2 mm i . d . x 80-100 mm) were heated i n a constant temperature bath (a 50:50 mixture of sodium n i t r a t e and potassium n i t r a t e ) equipped with a s t i r r e r and an N.B.S. c a l i b r a t e d thermometer. The pyrex tubing was washed with water and acetone and dried thoroughly before use. The progress of the reac t i o n was monitored by an Aerograph Model A-90-P3 v.p.c. (20% FFAP, 205°, 120 ml/ min) equipped with a thermal conductivity detector. A Honeywell Model E l e c t r o n i c 15 recorder having a d i s c chart i n t e g r a t o r was used to calculated the r a t i o of products. Straight l i n e f i t s were c a l c u l a t e d by the method of l e a s t squares using a Hewlett Packard 9100 Calculator equipped with a 9125 A Calculator P l o t t e r . Derivation of the rate constants are given i n - 157 -Appendix I. Equations used to c a l c u l a t e the a c t i v a t i o n parameters are given i n Appendix I I . The main source of err o r i s i n the maintainance of a constant temperature i n the range employed (250° to 290°C). Temperatures are considered to be accurate to + 0.4°C and a n a l y t i c a l p r e c i s i o n i s judged to be + 1.2% ( 77). Errors i n the rate constants are estimated to be + 5%, i n the a c t i v a t i o n energy E to be + 5%, and i n AS^ + 4 e.u. SL E q u i l i b r i u m p o s i t i o n s were measured at four d i f f e r e n t temperatures ranging from 262.5° to 314.8°C, eq. 70 . Other eq u i l i b r i u m p o s i t i o n s that were required were c a l c u l a t e d (see Table XXXVI). A l l e q u i l i b r i u m p o s i t i o n s were approached from both sides. Because of the small d i f f e r e n c e s i n the equilibrium p o s i t i o n s over a r e l a t i v e l y large temperature range, the equilibrium p o s i t i o n s were determined at one s i t t i n g . [ ? o ! w ~ A ; T V s - ^ C0CH 3 132 + 133 136 Table XXXVI. Equilibrium P o s i t i o n s f o r Equation [70]. Temperature (°C) 132:133 : 136 314.8 12.4 . 87.6 291.1 11.7 88.3 287.5 11.6 : 88.4 1 279.6 11.2 : 88.8 1 270.0 10.9 . 89.1 262.5 10.6 . 89.4 254.9 10.3 : 89.7 1 Calculated - 158 -I t was discovered that the progress of the re a c t i o n was h i g h l y dependent on the proportion of the volume of the rea c t i o n v e s s e l to the quantity of sample used, hereby designated as V/S. When the proportion of V/S was small, the conversion of the cyclopropyl ketones 132 + 133 to the dihydrofuran 136 was f a s t e r than when V/S was la r g e , eq. 71 , see Table XVI of the Results. In a d d i t i o n , when V/S was small, there was an appreciable amount of ct,8 - and B,Y~°l-ef i - n s formed; whereas, at a large V/S the o l e f i n formation was n e g l i g i b l e , eq. Moreover, at large values of V/S the percentage of dihydrofuran 136 [71] E-134 E-135 appeared to l e v e l o f f . I t was i n t h i s l e v e l l i n g o f f region that k i n e t i c studies were performed. In t h i s region reproducible r e s u l t s could be obtained, o l e f i n formation could be eliminated, and charring of thesample could be prevented. The rates and a c t i v a t i o n parameters are recorded i n Table XVII of the Results. - 159 -, (b) Cis and trans-l-acetyl-l-methyl-2-phenylcyclopropane (132) and (133) Addition of 8.4 g (0.1 mole) of methyl isopropenyl ketone to a petroleum ether s o l u t i o n of phenyldiazomethane (prepared from 0.1 mole of benzaldehyde hydrazone and 0.1 mole of yellow mercuric oxide (15)) caused immediate evolution of nitrogen. A f t e r 2 h, the red colour of the diazo compound had completely disappeared. Rotatory evaporation of the solvent followed by vacuum d i s t i l l a t i o n (90-95° at 0.3 mm Hz) yiel d e d 12.6 g of a s l i g h t l y yellowed s o l u t i o n . The v.p.c. (20% FFAP, 205°, 60 ml/min) indic a t e d two peaks i n a 1:2 r a t i o with respective r e t e n t i o n times of 7.7 and 9.3 minutes. The two peaks were separated and c o l l e c t e d by v.p.c. The f i r s t peak was i d e n t i f i e d by n.m.r. as the c i s isomer 132 and the second peak as the trans-isomer 133. For the c i s - c y c l o p r o p y l ketone 132: i . r . 1695, 1605, 725 and 697 cm"1; n.m.r. (60 MHz, CCl^) 8.33 and 8.54 x (s i n g l e t s ) a c e t y l and C - l methyls r e s p e c t i v e l y , 7.75 x ( t r i p l e t J * 7.7 Hz) C-2 hydrogen, 8.09 x (doublet of doublets J = 4.6 and 7.5 Hz) one C-3 hydrogen, 9.04 x (doublet of doublets J = 8.4 and 4.6 Hz) other C-3 hydrogen. Anal. Calcd. f o r C-^H^O: C, 82.76; H, 8.05. Found: C, 83.03; H, 8.25. For the trans-cyclopropyl ketone 133: i . r . 1690, 1605, 778 and 698 cm - 1; n.m.r. (60 MHz, CCl^) 7.87 and 8.98 x (s i n g l e t s ) a c e t y l and C - l methyls r e s p e c t i v e l y , 7.34 x (doublet of doublets J = 7.0 and 9.0 Hz) C - l hydrogen, 8.37 x (doublet of doublets J = 4.2 and 9.0 Hz) 1 Cis re f e r s to the C - l a c e t y l and C-2 phenyl. - 160 -one C-3 hydrogen, 8.94 T (doublet of doublets J = 4.2 Hz, other doublet obscured by C-3 methyl resonance) other C-3 hydrogen. Anal. Calcd. f o r C^H^O: C, 82.76; H, 8.05. Found: C, 82.54; H, 8.02. (c) 3-Methyl-5-phenyl-3- and -4-pentene-2-one Large s c a l e preparation of the t i t l e compounds was accomplished by heating s e v e r a l 50 \il samples of the cyclopropyl ketones 132 and 133 i n non-degassed sealed pyrex tubing ( i . e . 2.1 mm x 50 mm) at 250° fo r 8 h. The charred samples were bulb to bulb vacuum d i s t i l l e d (bath temperature 80-100° at 0.3 mm Hg). The product o l e f i n s were c o l l e c t e d together by preparative v.p.c. (20% FFAP, 205°, 60 ml/min). Their vapour phase chromatogram resembled two overlapping peaks at re t e n t i o n times 11.1 and 12.1 minutes. The n.m.r. (100 MHz, CCl^) was run on the mixture of products and was completely resolved. For the a,8-unsaturated ketone 134: 7.86 T ( s i n g l e t ) a c e t y l methyl, 8.19 x ( s i n g l e t showing long range coupling) C-3 methyl, 6.54 x (doublet J = 7.5 Hz) C-5 hydrogens, 3.34 x ( t r i p l e t showing long range coupling J = 7.5 Hz). For the 8,y-unsaturated ketone 135: 7.95 x ( s i n g l e t ) a c e t y l methyl, 8.82 x (doublet J = 7.0 Hz) C-3 methyl, 6.79 x (quintet J = 7.0 Hz) C-3 hydrogen, 3.89 x (doublet of doublets J = 8.0 and 16.0 Hz) C-4 v i n y l hydrogen, 3.53 x (doublet J = 16.0 Hz) C-5 v i n y l hydrogen. The r a t i o of the two o l e f i n s 134 and 135 was 3:2 r e s p e c t i v e l y . - 161 -(d) 2,3-Dimethyl-5-phenyl-4,5-dihydrofuran (136) Six 50 u £ samples of a mixture of the cyclopropyl ketones 132 and 133 i n degassed pyrex tubing (4.2 mm i . d . x 100 mm) were heated for 10 min at 335°. The s l i g h t l y charred samples were bulb to bulb vacuum d i s t i l l e d (bath temperature 85-100° at 0.5 mm Hg). The v.p.c. (20% FFAP, 205°, 60 ml/min) showed f i v e peaks. The f i r s t peak had a retention time of 5.1 min and the l a t t e r four had r e t e n t i o n times corresponding to the cyclopropyl ketones 132 and 133 and to the o l e f i n s 134 and 135. The 5.1 min peak was i s o l a t e d by preparative v.p.c. and i d e n t i f i e d as the t i t l e compound 136. For the dihydrofuran 136: i . r . 1701 cm - 1, u.v. (EtOH) end absorption only, n.m.r. (60 MHz, CCl^) 2.80 T (s i n g l e t ) phenyl hydrogens, 4.70 T (doublet of doublets J = 8.0 and 10.0 Hz) C-5 hydrogen, 6.7 to 7.8 T (multiplet) C-4 hydrogens, 8.26 and 8.40 t (si n g l e t s showing long range coupling ) C-2 and C-3 methyls. Anal. Calcd. f o r C^H^O: C, 82.78; H, 8.05. Found: C, 82.43; H, 8.25. (e) Attempted k i n e t i c s of c i s - t r a n s isomerization K i n e t i c rates and therefore a c t i v a t i o n parameters were not obtained f o r the c i s - t r a n s isomerization of the cyclopropanes 132 and 133. The reason f o r not obtaining these data i s due to the lack of r e p r o d u c i b i l i t y of the r e s u l t s . To c i t e one example, runs made at 225.0°C f o r 12.0 hours s t a r t i n g from the pure c i s - c y c l o p r o p y l ketone 132 gave the isomeric trans-- 162 -cyclopropane 133 i n y i e l d s varying from 47.6 to 65.1 percent. This d r a s t i c d i f f e r e n c e i n the degree of conversion to 133 represents a d i f f e r e n c e i n rates of about 100%. S i m i l a r r e s u l t s were obtained i n other experiments. In one case the conversion to the cyclopropane 133 from 132 ranged from 16.7 to 41.0 percent. In another, the range-was from 46.8 to 57.5 percent. - 163 -BIBLIOGRAPHY 1. (a) K.L. Rinehart and T.V. Van Auken. J. Amer. Chem. Soc., 82, 5251 (1960). (b) T.V. Van Auken and K.L. Rinehart. J. Amer. Chem. Soc, 84, 3736 (1962). 2e (a) CG. Overberger and J.P. Anselme. J. Amer. Chem. Soc, 86, 658.(1964). (b) CG. Overberger, R.E. Zangaro, and J.P. Anselme. J. Org. Chem., 31, 2046 (1966). 3o (a) CG. Overberger, N. Weinshenker, and J.P. Anselme. J. Amer. Chem. 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Consolidated Printers, Oakland, California, 1967, p. 132. - 168 -APPENDIX I Let the concentration of A = a and B = b at t = 0 Let the concentration of A = a-x and B = b+x at t = t This gives the d i f f e r e n t i a l rate equation: dx = k^a-x) - k_ 1 (b+x) or where dx = (k + k ) (m-x) dt 1 l k^a - k jb k l + k - l I n tegration gives: In 2 — = (k. + k , ) t m-x 1 - 1 or log m m-x (k x + k_ 1) 2.303 - 169 APPENDIX II or d In k _ dt " RT -E /RT k = Ae 3 E 3. In k = In A - — E log k = log A - 2 7 3 ^ 1 E a Pl o t log k vs. — gives slope = -in t e r c e p t = log A E a = -2.3 R (slope) AH + = E - RT a AS + = 2.3 R log — + 2.3 R log ^ V = -61.7 + 4.574 log A - 170 -APPENDIX I I I -3.60 -i -3.80 H 4.00 A 4.20 H -4.40 H 4.60 -\ 4.80 H •5.00 i 1 1 1 1 1 1.75 1.79 1.83 1.87 1.91 1.95 - 171 -APPENDIX IV A^e -E^RT A 2e -E 2/RT A^e -E 1/RT A 2e -E 2/RT A l E 2 ~ E 1 / R T k A E - E £ n k j - + - h 1 A l E 2 - E l l o g A j + 2TTRT 1 1 A plot of log r — vs. — gives a straight line with a slope of V E i 2 2 R a n c* 311 i-nterceVt of log 1— • - 172 -

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