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Stereochemistry of olefin formation in the pyrolysis of 3-carbomethoxy pyrazolines Wu, Weh-Sai 1966

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STEREOCHEMISTRY OF OLEFIN FORMATION IN THE PYROLYSIS OF 3-CARBOMETHOXY PYRAZOLINES BY WEH-SAI WU B.Sc, Chung-Hsing University, 1962 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE in the Department of Chemistry We accept this Thesis as conforming to the required standard. THE UNIVERSITY OF BRITISH COLUMBIA September, 1966 In presenting t h i s thesis i n p a r t i a l f u l f i l m e n t of the requirements for an advanced degree at the University of B r i t i s h Columbia, I agree that the Library s h a l l make i t f r e e l y available for reference and study, I further agree that permission, for extensive copying of t h i s thesis for scholarly purposes may be granted by the Head of my Department or by his representatives, I t i s understood that copying or publication of t h i s thesis for f i n a n c i a l gain s h a l l not be allowed without my written permission. The University of B r i t i s h Columbia Vancouver 8 5 Canada Department of ABSTRACT The thermal decomposition of cis- and trans-3-methyl-4-ethyl-3-carbo-methoxy-A^pyrazoline (cis- implies that the methyl and ethyl groups are cis) and trans-3-methyl-4-ethyl-3-carbomethoxy-A1-pyrazoline gave a mixture which contained cyclopropane products, cis- and trans-l-methyl-2-ethyl-l-carbo-methoxycyclopropane; a, B-unsaturated ester products, methyl cis- and trans-2,3-dimethyl-2-pentenoate (cis and trans refer the two methyl groups); and the 6 ^ -unsaturated ester, methyl 2-methyl-3-ethyl-3-butenoate. The a,B-unsaturated esters are formed stereospecifically since cis-3-methyl-4-ethyl-3-carbomethoxy-A1-pyrazoline gave only methyl trans-2,3-dimethyl-2-pentenoate (56% in £he liquid phase and 28% in the vapor phase). Similarly in the pyrolysis of trans-3-methyl-4-ethyl-3-carbomethoxy-A1-pyra-zoline methyl cis-2,3-dimethyl-2-pentenoate (13% in the liquid phase and 6% in the vapor phase) was obtained while only a trace of methyl trans-2,3-dimethyl-2-pentenoate was found in both the liquid and vapor phase pyrolysis. The cyclopropane products formed from pyrolysis of cis- and trans-3-methyl-4-ethyl-3-carbomethoxy-A1-pyrzaoline have shown some degree of stereo-specificity with a predominance of the isomer having the same stereochemistry as the starting pyrazoline being obtained. The results of the above experiments suggest that the mechanism of thermal pyrolysis of pyrazolines requires that the nitrogen leaves from the same side as the ethyl group, i.e. trans to the hydrogen which is migrating. The photolysis of cis- and trans-3-methyl-4-ethyl-3-carbomethoxy-A1-pyrazoline has been found to be stereospecific in cyclopropane formation with the absence of isomeric olefin products. A small amount of the olefin corres-ponding to loss of CH2N2 was also found having the same stereochemistry as the pyrazolone. Since the products from photolysis are different from that of pyrolysis, a modified mechanism is required. Insufficient evidence available to clearly define that mechanism. iv TABLE OF CONTENTS Page I. Introduction 1 Preparation of Pyrazolines 1 Pyrolysis of Pyrazolines 3 Photolysis of Pyrazolines 10 II. Results 14 Synthesis of cis- and trans-3-Methyl-4-ethyl-3-carbomethoxy-A*-pyrazolines 14 Separation of Methyl cis- and trans-2-Methyl-2-pentenoate .. 15 Pyrolysis of cis- and trans-3-Methy1-4-ethyl-3-carbomethoxy-A^-pyrazolines 16 Photolysis of cis- and trans-3-Methyl-4-ethyl-3-carbomethoxy-A^pyrazolines 17 Compound Identification 18 a. Infrared Spectra 18 b. N.M.R. Spectra 19 III. Discussion ^ Steric Conformation of Pyrazoline Rings 24 Considerations of Possible Mechanism for the Pyrolysis Reaction 28 Mechanism of the Photolysis Reaction 32 IV. Experimental 34 Experimental Instruments and Procedures 34 Sample Preparation 34 a. Preparation of N-Nitroso-N-methylurea 34 b. Preparation of N-Nitroso-N-ethylurea 34 c. Preparation of Diazomethane , 35 d. Preparation of Diazoethane 35 e. Preparation of cis- and trans - 3,5 -Dimethyl- 3- carbq:-methoxy-A^pyrazolines 35 V TABLE OF CONTENTS (cont'd) Page Liquid Phase Pyrolysis of S^-Dimethyl-S-carbomethoxy-A1-pyrazolines 37 Separation of Methyl cis- and trans_-2-Methyl-2-pentenoate .... 37 a. Separation of Methyl trans-2-Methy1-2-pentenoate 37 b. Separation of Methyl cis-2-Methyl-2-pentenoate 38 Preparation of cis- and trans-3-Methyl-4-ethyl-3-carbomethoxy-A^pyrazolines 38 a. Preparation of cis-3-Methyl-4-ethyl-3-carbomethoxy-A1-pyrazoline 3 8 b. Preparation of trans-3-Methyl-4-ethyl-3-carbomethoxy-A1-pyrazoline 39 Pyrolysis and Photolysis of cis- and trans-3-Methyl-4-ethyl-3-carbomethoxy-A^pyrazolines . 40 a. Liquid Phase Pyrolysis of cis-3-Methyl-4-ethyl-3-carbo-methoxy-A^pyrazolines 40 b. Vapor Phase Pyrolysis of cis-3-Methyl-4-ethyl-3-carbo-methoxy-A^pyrazolines 41 c. Photolysis of cis-3-Methyl-4-ethyl-3-carbomethoxy-A1-pyrazolines 42 d. Liquid Phase Pyrolysis of trans-3-Methyl-4-ethyl-3-carb,o-methoxy-A^pyrazolines 43 e. Vapor Phase Pyrolysis of trans-3-Methyl-4-ethy1-3-carbomethoxy-A^pyrazolines 44 f. Photolysis of trans-3-Methy1-4-ethy1-3-carbomethoxy-A1-pyrazolines 45 Bibliography 47 Appendix (n.m.r. Spectra) 49 v i LIST OF TABLES Table I. The n.m.r. Data of cis- and trans-3-Methyl-4-ethyl-S-carbomethoxy-A^pyrazolines 20 II. The n.m.r. Data of Methyl cis- and trans-2,3-Dimethyl-2-pentenoate 21 III. The n.m.r. Data of cis- and trans-^l-Methyl-2-ethyl-l-carbomethoxycyclopropanes 22 IV. D i s t i l l a t i o n Fractions in the Separation to yield 36 Methyl cis- and trans-2-Methyl-2-*pentenoate V. Purification of trans-2-Methyl-2-pentenoate by Di s t i l l a t i o n 37 VI. Attempted Purification of cis-2-Methyl-2-pentenoate by D i s t i l l a t i o n 38 v i i LIST OF FIGURES Figure Page I. Preparation of 1-Methyl-l-carbomethoxycyclopropane ...... 1 II. Mechanisms Proposed for Pyrazoline Formation 2 III. Synthesis of cis- and trans-3,4-Dimethy1-3-carbomethoxy-A^pyrazolines 2 IV. C-N Bond Breaking During Pyrolysis of Pyrazolines 3 V. Thermal Pyrolysis of cis- and trans_-3,4-Dimethyl-3-carbomethoxy-A^pyrazolines , 4 VI. Free Rotation in the Intermediate of the C-3-C-4 Bond.... 5 VII. Pyrolysis of trans-3,5-Diphenyl-A^pyrazoline 5 VIII. Liquid Phase Pyrolysis of cis- and trans-3,5-Dimethyl-3-carbomethoxy-A^pyrazolines 6 IX. Intermediate Showing Concerted Hydrogen Migration 7 X. Kinetic Studies for Pyrolysis of 4-Methyl-A1-pyrazoline and its C-4 Deuterated Substituent 8 XI. Tr-Cyclopropane Intermediate 8 XII. Pyrolysis of cis- and trans-3,5-Dimethyl-A1-pyrazolines . 8 XIII. Intermediates from cis- and trans^.S-Dimethyl-A1-pyrazolines 9 XIV. Conrotation and Disrotation 9 XV. Photolysis of cis- and trans_-3j,5-Dimethyl-3-carbomethoxy-A^pyrazolines 11 XVI. Possible Transition States in Photolysis of 3,4-Dimethyl-3-carbomethoxy-A^pyrazolines . • • • • H XVII. Photolysis of cis- and trans-3,5-Dimethyl-3-carbo-methoxy-A1-pyrazolines 12 XVIII. Possible Pyrolysis Reactions of cis- and trans-3-Methy1-4-ethyl-3-carbomethoxy-A1-pyrazolines 13 XIX. Preparation of cis- and trans-3-Methyl-4-ethyl-3-carbo-methoxy-A^pyrazolines 14 XX. Synthesis of cis- and trans-3,5-Dimethy1-3-carbomethoxy-A^pyrazolines 15 v i i i LIST OF FIGURES (cont'd) Figure Page XXI. Liquid Phase Pyrolysis of a Mixture of cis- and trans-S.S-Dimethyl-S-carbomethoxy-A^pyrazolines 15 XXII. Pyrolysis of cis- and trans-3-Methy1-4-ethy1-3-carbo-methoxy-A^pyrazolines 17 XXIII. Photolysis of cis- and trans-3-Methy1-4-ethy1-3-carbo-methoxy-A^pyrazolines 18 XXIV. Ring Opening of trans-1-Methvl-2-ethvl-1-carbomethoxv-cyclopropane 23 XXV. Conformation of the Pyrazoline Ring 24 XXVI. Axial and Equatorial Hydrogens at the C-5 Position of the Pyrazoline Ring , 26 XXVII. Dihedral Angles of He-Hc_4 and HQ-H^ of the Pyrazoline 26 XXVIII. Prefered Conformation of cis- and trans-3-Methy1-4-ethyl-S-carbomethoxy-A^pyrazolines . 27 XXIX. Transition States for a,B-Unsaturated Esters Formation .. 28 XXX. Pyrolysis of cis, trans- and cis,cis-3,4,5-Trimethyl-3-carbomethoxy-Ai-pyrazolines 29 XXXI. Intermediate with a Pair of p-Orbitals '. 30 XXXII. Cyclopropane Intermediates of Pyrolysis of cis- and trans-3-Methyl-4-ethyl-3-carbomethoxy-A1-pyrazolines ... 31 XXXIII. Ionic Mechanism for the Pyrolysis of 3-Methyl-4-ethyl-3-carbomethoxy-A1-pyrazoline 32 XXXIV. Transition States of Photolysis 33 XXXV. Bulb to Bulb D i s t i l l a t i o n Apparatus 39 XXXVI. Vapor Chromatogram of the Product from the Liquid Pyrolysis of cis-3-Methyl-4-ethy1-3-carbomethoxy-A1-pyrazoline 41 XXXVII. Vapor Chromatogram of the Product from the Vapor Pyrolysis of cis-3-Methyl-4-ethyl-3-carbomethoxy-A1-pyrazoline . 42 XXXVIII. Vapor Chromatogram of the Product from the Photolysis of cis-3-Methyl-4-ethy1-3-carbomethoxy-A1-pyrazoline .. 42 ix LIST OF FIGURES (cont 1d) Figure Page XXXIX. Liquid Phase Pyrolysis of trans-3-Methyl-4-ethyl-3-Carbomethoxy-A^-pyrazoline 43 XL. The Product Distribution from Thermal Pyrolysis of trans-3-Methy1-4-ethyl-3-carbomethoxy-A1-pyrazolone with Reduced Attenuation 44 XLI. Product. Distribution of the Product from the Vapor Phase Pyrolysis of trans-3-Methy1-4-ethyl-3-carbomethoxy-A^pyrazoline 45 XLII. Product Distribution of the Product from the Photolysis of trans-3-Methy1-4-ethyl-3-carbomethoxy-Ai-pyrazoline 45 X ACKNOWLEDGEMENT The author wishes to express his gratitude to Dr. D.E. McGreer, his research supervisor under whose direction and encouragement this research was performed. The author would also like to express his gratitude to Mrs. A. Brewster for the nuclear magnetic resonance spectra, to Mr. P. Borda and Mr. A. Bernhardt for the microanalyses. The financial assistance of the National Research Council of Canada for this research program is deeply appreciated. - 1 -INTRODUCTION A route that has been known for some time for the preparation of cycloproparie derivatives i s based on the synthesis of A^pyrazolines by the addition of a diazoalkane to an a,g-unsaturated ester (1-3) followed by pyrolysis of the pyrazoline at temperatures from 100-200°C (4-6). For example, 1-methyl-l-carbomethoxycyclopropane (III) can be made (7) as shown in the Figure I. CH 3 I CH 2N 2 + CH2 =C-C02CH3 C0 2CH 3 II CH3 C0 2CH 3 CH3 V H CH3 _A -tn C0 2CH 3 I I I 65% IV 15% H 1 _ CH3 CH3 Cp 2CH 3 V 15% Figure I. H H -'C02CH3 \ i / + C C CH 2^ ^ CH3 VI 5% Preparation of 1-Methyl-l-carbomethoxycycoJlpropane. In addition to cyclopropane products there are usually also formed a,g-and g,y-unsaturated ester products. It i s the purpose of this thesis to examine t h i s reaction i n some d e t a i l i n the hope that a better understanding of the mechanism of th i s pyrolysis reaction w i l l r e s u l t . Preparation of Pyrazolines The addition reaction of a diazoalkane to the a,3-unsaturated carbonyl compound to form a A^pyrazoline has recently been suggested to be a one-step - 2 -multiple centre reaction (8,9) rather than a two-step mechanism (10) suggested earlier. The basis of this suggestion has been due to the absence of the isomeric A^pyrazoline in a synthesis where two isomers should be possible by the two-step mechanism. The two proposed mechanisms are shown in Figure II and an example illustrating the cis addition/diazomethane with formation of a single pyrazoline product is shown for the addition to methyl tiglate (IV) and methyl angelate (V) to give cis- and trans-3,4-dimethyl-3-carbomethoxy-A^pyrazolines (XI and XII) (11) respectively as shown in Figure III. >C - C - \ jfLU R>L —-VII >C=C-C0- +RR'CN2 R R 7 N V >C C0-R=R'=H R=R* or R^ R' R' VIII Figure II. Mechanisms Proposed for Pyrazoline Formation. This feature of the pyrazoline synthesis provides a means to obtaining isomeric pyrazolines differing only in their geometrical configura-tions like IX and X. CH3 CH3 < r H N C02CH3 IV H CH; C02CH3 + CH2N2 •+ CH2N2 CH: H ^  IX CH^  CH3 "" C02CH3 N ^ 1 CH-. C02CH3 V Figure III. Synthesis of cis- and trans-3,4-Dimethy1-3-carbomethoxy-A^pyrazolines. - 3 -Other pairs of geometrical isomers have been obtained by separation of the pyrazoline pair prepared as a mixture by d i s t i l l a t i o n , vapor chromato-graphy and crystallization. The cis- and trans-3,5-dimethyl-3-carbomethoxy-A^pyrazolines (XL and XII) were separated by d i s t i l l a t i o n (12). cis- and trans -3,5-dimethyl-A1-pyrazoline (XIII and XIV) were separated by vapor chromato-graphy (13) and cis- and trans-3,5-di- (pr-anisyiyA1 -pyrazoline (XV and XVI) were separated by crystallization (14). CH, fco2 C02CH3 CH3 1""C02CH3 XI CH3" XIII ^CH3 T CH3 **VN ^ XII CH* CH :6H.0CH3-p XIV N p TCH 30C 6 Hi+ V XV p-0CH3C6Hi4 f .C6HL,0CH3-P XVI Pyrolysis of Pyrazolines Early suggestions concerning the mechanism for the pyrolysis of pyrazolines have involved intermediates resulting from bond breaking of one or both1 of the C-N bonds as shown in Figure IV. Figure IV. C-N Bond Breaking During Pyrolysis of Pyrazolines, - 4 -Thus ionic or free radical species (10,15,16,17) have been considered which by hydrogen migration can give olefin products and by ring closure can give cyclopropane products. Some recent experimental results leading to mechanistic suggestions are given below. Van Auken and Rinehart (11) - Thermal pyrolysis of cis-3,4-dimethyl-3-carbomethoxy-A^pyrazoline (IX) gave as decomposition products cis-1,2-dimethyl -1-carbomethoxycyclopropane (XVII), trans-1.2-dimethvl-l-carbomethoxvcvclo-propane (XVIII), methyl 2,3-dimethyl-2-butenoate (XIX) and methyl 2,3-dimethyl-3-butenoate (XX) in the ratio of 17.6 %, 12.3 %, 65.8 %, 4.3 % whereas in the pyrolysis of trans-3,4-dimethyl-3-carbomethoxy-A1-pyrazoline (X), the ratio of these products were 28.4 %, 34.6 %, 32.9 %, 4.1 % respectively as shown in Figure V. CH^ ^CHg CRj >CH3 CH3^  CH3 CH3 H CH3 r*C02CH3 "\ /''CO2CH3 CH, .CH CHf C02CH3 CH2 C02CH3 IX C H 3""- G„CO2CH3 3 ""C02CH3 XVII XVIII XIX xx 17.6% 12.3% 65.8% 4.3% >CH 3 —p/( 02( 28.4% 34.6% 32.9% 4.1% N ^ N Figure V. Thermal Pyrolysis of cis- and trans-3,4-Dimethyl-3-carbomethoxy-A1-pyrazolines That these two pyrazolines (IX and X) gave almost a 50:50 mixture of cis- and trans-cyclopropanes (XVII and XVIII) respectively suggested to the authors that the intermediate (XXI) has free rotation around the C-3-C-4 bond as shown in Figure VI. - 5 -CH: CH3 sC0 2CH 3 CH 3s ^ H 3 * C02CH3 cyclopropane IX and X XXI Figure VI. Free Rotation in the Intermediate of. the:C-3,-C-4 Bond. Overberger (18) - Thermal pyrolysis of trans-3,5-diphenyl-A 1-pyrazoline (XXII, n = 1) gave only trans-1,2-dipheny1eye1opropane. On the other hand, larger ring derivatives gave cis and trans products. Assuming a free radical intermediate (XXIV), Overberger e_t al^ suggest that the intermediate has much less time to become free to rotate in the formation of cyclopropane than in the case of formation of the cyclopentane or the cyclohexane products as shown in Figure VII. >>* * XXII n = 1 XXIII (CH2) •-f 'A <f>v N n = 3,4 (CH2 N n = 1,3,4 XXII (CH ) ( C H 2 ) n •,.,Z v * * ^ — V n = 3,4 -N2 (CH2T XXIV n • 3,4 product Figure VII: Pyrolysis of trans-S^-Diphenyl-A^pyrazoline. - 6 -In a later paper ( 1 4 ) , however, they have observed results that do suggest free rotation in the intermediate. ( c i s - 3 , 5 - D i ^ (p-ahisyl)-A 1-pyrazoline (XV) on pyrolysis gives a product containing 4 3 . 0 % of the cis cyclopropane and 57 % of the trans). McGreer and coworkers (12) - Thermal pyrolysis of cis- and t r a n s - 3 , 5 -dimethyl-S-carbomethoxy-A^pyrazolines (XI and XII) gave the products c j s - 1 , 2 -dimethyl-l-carbomethoxycyclopropane (XVII), trans-1.2-dimethyl-1-carbomethoxy-cyclopropane (XVIII), methyl cis -2-methyl -2-pentenoate (XXV), methyl trans - 2 -methyl-2-pentenoate (XXVI) and methyl 2-methyl-3-pentenoate (XXVII) in the ratio of 18 %, 48 %, 32 %, 0 %, 2 % and 60 %, 15 %, 0 %, 22 %, 3 % respect-ively as shown in Figure VIII. C 2H 5 C02CH3 H C02CH3 CH C02CH3 f CH3 C02CH3 A 3 XVII XVIII XXV XXVI XXVII ™ V ^ x , ^ r i ^ u i d 18% 48% 32% 0% 2% CH 3^ phase XI .CH3 f ^COzCHa A CH. liquid phase 60% 15% 0% 22% 3% XII Figure VIII. Liquid Phase Pyrolysis of cis- and trans_-3,5-Dimethyl-3-carbomethoxy-A1-pyrazolines. The major cyclopropanes (XVII and XVIII) obtained have the stereo-chemistry opposite to pyrazoline from which they were formed respectively, (XI and XII), and the olefins are formed by a stereospecific process. This therefore suggests a concerted hydrogen migration with loss of nitrogen in the olefin forming step as illustrated by the intermediate shown in Figure IX. Figure IX. Intermediate Showing Concerted Hydrogen Migration. Crawford and Mishra (13) - Kinetic studies for pyrolysis of 4-methyl-A^pyrazoline (XXIX) and it's C-4 deuterated substituent (XXX) gave a cyclo-propane and an olefin product in a nearly 50:50 ratio. The kinetic deuterium effect was 1.07 while the effect of deuterium on the product forming step indicated a kinetic isotope effect for step III of 1.80 (see Figure X). This suggests that the hydrogen migration takes place after the rate determining transition state and suggests an intermediate common to both cyclopropane and olefin formation. The structure of the intermediate has been suggested to be a planar symmetric molecule with a ir-bond between two of the carbons in the cyclopro-pane ring. This so called "TT-cyclopropane" is shown in Figure XI. Pyrolysis of c^s-S^-dimethyl-A^pyrazoline (XI) gave cis-l,2-dimethyl cyclopropane (XVII), trans-1,2-dimethylcyclopropane (XVIII) and trans-2-pentenoate (XXXIV) in the ratio of 33.24 %, 66.08 %, 0.68 % whereas the pyrolysis of trans- 3,5-dimethyl-A1-pyrazoline (XIV) gave the cis-2-pentenoate ro (XXXV) in addition to the above three p//ducts in the ratio of 72.61 %, 25.42 1.08 % and 0.91 % by the order of compounds XXXII, XXXIII, XXXIV, and XXXV as shown in the Figure XII. H(D) CH: XXIX H at C-4 XXX D at C-4 I XH k H . M i l - 8 Intermediate VH D /kinetic XH D / products II CH3 H(D) H(P). I l l = 1.07 = 1.80 A CH3-C-CH:3(D) Figure X. Kinetic Studies for Pyrolysis of 4-Methyl -A 1 -pyrazoline and i t s C-4 Deuterated Substituent. \ N \- _ ..M Figure XI. Tr-Cyclopropane Intermediate. CH. CH: CH: C H 3 * ^ N^ -XIII N XXXII 33.24% C H 3 ^ \ N ^ N XIV 72.61% XXXIII 66.08% CH H CH3 C2H5 H xxxrv 0.68% 1^  CH3 C2H5 Cfl 3 C2HS5 ft H: 25.42% 1.08% XXXV 0.91% Figure XII. Pyrolysis of cis- and trans-S.S-pimethyl -A 1 -pyrazoline. Loss of nitrogen from XIII would be expected to give intermediate XXXVI which by hydrogen migration from C-4 to C-3 or C-5 can only give trans-2-pentene (XXXIV). However, in the intermediate XXXVII expected from XIV hydrogen migration from C-4 to C-3 would give trans-2-pentenp (XXXVI) and from C-4 to C-5 would give cis-2-pentene (XXXV) as shown in Figure XIII. CHc P * 3 XIII CHc r XT * CH, ^N'" XIV C H 3 H 2 C H 3 H H XXXVI 5 3 H CH3 XXXVII Figure XIII. Intermediates from cis- and trans-3,5-Dimethyl-A^pyrazolines. These two p-orbitals at C-jf andC-3 of intermediates X X X V I and X X ^ V J J I form a weak n-bond. Conversion of this TT-bond to a a-bond is possible by two forms' of internal rotation. These are defined as conrotation and dis-rotation as shown in Figure X I V . Conrotation Disrotation Represents,a p-orbital Figure XIV. Conrotation and Disrotation. - 1 0 -Quantum mechanical evaluation of the symmetry changes in going from the IT type bond to a a-bond suggests that conrotation would be more favored than disrotation (19). The experimental results of Crawford (13) and McGreer (12) when evaluated in terms of this mechanism show a preference to conrotation. On the other hand, Overberger's (18) results do not. Photolysis of Pyrazolines Irradiation of A ^ pyrazolines at the wave length of their absorption (about 320 my with e , of 500) results in loss of nitrogen and products mol. similar to the products from pyrolysis. Major differences in the stereochemi-cal results for the cyclopropane formation, however, suggest that here a new or modified mechanism is involved. Results of significance are the following however, no attempt has been made to identify the species which is fragmenting (i.e. whether i t is an excited state or a high energy ground state molecule etc.). Van Auken and Rinehart (11) have observed the photolysis of cis-and trans-S^dimethyl-S-carbomethoxy-A^pyrazoline (IX and X) to give as main products cis- and trahs-1,2-dimethyl cyclopropane derivatives (XVII and XVIII) with the same geometrical configuration as the pyrazoline from which they were obtained. Additional compounds in the products were identified as the a,3-unsaturated esters, methyl tiglate (IV) and methyl angelate (V) respectively resulting from loss of CH2N2 from the pyrazoline. The other products found in the pyrolysis reaction were present in only trace amounts as shown in Figure XV and therefore suggested a molecular reaction. The transition states in photolysis have been suggested to be either XXXVIII or XXXIX in the Figure XVI. - 11 -CH3 CH3 CH3 CH3 ft C02CH3 "£C02CH3 + CH3 CH 3 H^~1X)2CH3 + trace of other products IX XVII IV CH 3%. CH3 'C02CH3 CH X p 3 *"C02CH3 H CH3 A w + trace of other CHf \o 2CH 3 products XVIII Figure XV. Photolysis of cis- and trans-3,4-Dimethy1-3-carbomethoxy-A^pyrazolines. C0 2CH 3 CH3 CH3 t p r r r r r r T ! < : c o 2 c H 3 XXXVIII XXXIV Figure XVI. Possible Transition States of Photolysis in 3,4-Dimethy1-3-carbomethoxy-A^pyrazoline. McGreer e_t al (12) have observed the photolysis of cis- and trans-3/^ /methylvf-^^^!'-3-carbomethoxy-A1-pyrazolines (XI and XII) to give the products with the proportional distributions as shown in the Figure XVII. The cyclopropane products in contrast to the pyrolysis results are predominantly of the same stereochemistry as the starting pyrazoline. It was - 12 -therefore suggested that the fragmenting molecule is a "hot ground state molecule" which due to i t s high energy is reacting from a different average conformation than in the thermal reaction. \ H CH3 C0 2 C H 3 C H | \ / % ) 2 C H 3 1=^  \/ c2rig C0 2 C H 3 XVII XVIII XXV XI e t h e r , 35° 61% 23% 6% sth( 35' XII e ^ o r > 22% 65% 0% C 2 H 5 C H 3 H H C H 3 V=£ V - ^ C H 3 C H 2 = < ; (J0 2 CH 3 C H 3 C H C0 2 C H 3 C02CH3 XI XII XXVI XXVII I ether 35° 2% 2% 6% ether . 35° 5% 2% 6 Figure XVII. Photolysis of cis- and trans-3,5-Dimethyl-3-carbomethoxy-A1-pyrazolines. Because of the stereospecificity observed by McGreer et ^1 in the formation of the a,8-unsaturated products for the pyrolysis of cis- and trans-3,5-dimethyl-3-carbomethoxy-A1-pyrazolines (XI and XII) (12) i t was proposed that this phase of the reaction could be studied further by exam-ining a pyrazoline pair related to those studied by Van Auken and Rinehart (11). The olefins obtained by Van Auken and Rinehart are symmetrical and ro thus Tp//vide l i t t l e information for the olefin-forming reaction. By working with an ethyl group at C-4 rather than a methyl both cis and trans-a,8-unsaturated products are possible as shown in Figure XVIII. - 13 -C2H5 CH3 Figure XVIII. Possible Pyrolysis Reactions.of cis- and trans-3-Methyl-4^ethyl-3-carbomethoxy-A1-pyrazolines. - 14-II RESULTS Synthesis of c i s - and trans-3-Methyl-4-ethyl?3-carbomethoxy-A 1-pyrazolines  (XL and XLI). The c i s - and trans-3-methyl-4-ethy1-3-carbomethoxy-A 1-pyrazolines (XL and XLI) were synthesized by adding diazomethane to methyl trans- and cis-2-methy1-2-pentenoate (XXVI and XXV) respectively as shown i n the Figure XIX. C2H5 Ctt$ W t 0 2CH 3 XXVI H CH3 C2H5 C02CH 3 XXV CH2N2 CH 2N 2 2 n5 H C 2 H 5 * CH3 *'C02CH3 XL • C H3 "' C0 2CH 3 XLI Figure XIX. Preparation of c i s - and trans-3-Methy1-4-ethy1-3-carbomethoxy-A 1-pyrazolines. The c i s - and trans_-'2-methylT2-pentenoate (XXV and XXVI) used were isolated from the pyrolysis i n the l i q u i d phase of a mixture of c i s - and trans-3,5-dimethy1-3-carbomethoxy-A 1-pyrazolines (XLIII) which were synthe s i z e d from methyl methacrylate (I) and diazoethane (XLII) (20) as shown i n the Figure XX. The n.m.r. spectra showed the mixture to contain two isomeric pyrazolines; trans-3,5-dimethy1-3-carbomethoxy-A^pyrazoline (XII) 64% and cis-S^-dimethyl-S-carbomethoxy-A^pyrazoline (XI) 36 %. Thermal pyrolysis of the pyrazoline mixture XLIII i n the l i q u i d phase without solvent at a temperature about 90° to 120°C gave f i v e products which - 15 " have been identified earlier (20 and 12) and are illustrated together with the percentage distributions in Figure XXI. CH3 H2C=C-C02CH3+ CH3CHN2 XLII CHc CH. N C02CH3 36% XI T L I I T CH rf CH3 C02CH3 64% X I I XLII I Figure XX. Synthesis of cis- and trans - 3,5- Dimethyl - 3- carbomethoxy -. A 1-pyrazolines. CH CH3 H v A ~ V',."C02CH3 C H« XVII 45% XVIII 27% C 2H 5 CH3 H*v to 2CH 3 XXVI 15% • H C H 3 A A C2H5^X fj0 2 C H 3 XXV 10% H C H 3 C H ' H C H 3 C0 2 CH 3 XXVII 3% Figure XXI. Liquid Phase Pyrolysis of Mixture of cis- and trans-3,5-Dimethyl-3-carbomethoxy-A1-pyrazolines. Separation of Methyl cis- and trans-2-Methyl-2-pentenoate The product from pyrolysis of mixture XLIII was d i s t i l l e d using an annular Teflon spinning-band d i s t i l l a t i o n column with an automatic reflux ratio controller under atmosphere pressure. The residue contained 90.2 % methyl trans_-2-methyl-2-pentenoate (XXVI) and 9.8 % cis-1,2-dimethyl-1-5, carbomethoxycyclopropane (XVII) and re d i s t i l l a t i o n of this residue, give/pure - 16 -XXVI in a yield of 11.4 % based on pyrazoline used. It was impossible to completely purify the methyl cis-2-methyl-2-pentenoatq (XXV) by the d i s t i l l a t i o n method. It was obtained pure by gas chromatographic separation of the enriched fractions with a final percentage yield of 4%. The methyl cis- and trans-2-methyl-2-pentenoate (XXV and XXVI) were reacted wi;th excess diazomethane respectively and in a few days gave trans -and cis-3-methy1-4-ethyl-3-carbomethoxy-A1-pyrazolines (XLI and XL) respectively. Pyrolysis of cis- and trans-.3-Methylf4-ethylr-3-carbomethoxy-A1-pyrazolines The products isolated from the pyrolysis of these pyrazolines (XL and XLI) and their distributions as measured by chromatography are given in the Figure XXII. Some features of interest in the results are the following. Pyrolysis of cis-3-methyl-4-ethyl-3-carbomethoxy-A^pyrazoline (XL) without solvent around 115° to 145°C gave as the major product methyl trans-2,3-dimethyl-2-pentenoate (XLIV) (56 % ) . None of the isomeric unsaturated olefin cis-2,3-dimethyl-2-pentenoate (XLV) was formed. Both cyclopropane products cis-1-methy1-2-ethyl-l-carbomethoxycyclopropane (XLVI) (31 %) and trans-l-methyl-2-ethyl-1-carbomethoxycyclopropane (XLVII) (9 %) were formed with the major isomer having the same stereochemistry as the starting, pyrazoline. Methyl 2-methyl-3-ethyl-3-butenoate (XLVIII) (4 %) was found as a minor product. On the other hand, liquid phase pyrolysis of a neat sample of trans-3-methyl-4-ethyl-3-carbomethoxyrA1-pyrazoline (XLI) at around 105° to 140°C gave cis-2,3-dimethyl-2-pentenoate (XLV) (13 %) as the a,g-unsaturated olefin product. The percentage of the cyclopropane derivatives (XLVI and XLVII) and the 6,y-unsaturated olefin (XLVIII) were 11 %, 72 % and 4 % respectively with - 17 -again a tendency for retention of stereochemistry in the cyclopropane product. Similar results were obtained for the vapor phase pyrolysis and are also shown in the Figure XXII. Photolysis of cis- and trans-3-Methyl-4-ethyl-3-carbomethoxy-A1-pyrazolines Ultraviolet irradiation of cis- and trans-3-methyl-4-ethy1-3-carbo-methoxy- A ^ pyrazolines (XL and XLI) gave as the main products cis- and trans-l-methyl-2-ethyl-1-carbomethoxycyclopropanes (XLVI and XLVII) respectively and each of the two isomeric pyrazolines gave a small amount of the ct,8-unsatu-rated olefin corresponding to stereospecific loss of CH2N2 as shown in Figure XXIII. C 2H 5 CH3 CH3 CH3 > -ft* I f t0 2CH 5 C2H5** "to2a\s XLIV XLV I P XL • , r ' > 56% V.P. t 28% C02CH3 L P XLI — ' — ^ trace 13% 11% V.P- , trace 6% 18% C2Hg H CH2 C02CH3 XLVII XLVIII XL 9% 4 % V.P. , 19% 6% XLI L , P > 72% 4 % V.P. 74% 2\ Figure XXII. Pyrolysis of cis- and trans-3-Methyl-4-ethy1-3-carbomethoxy^A1-pyrazolines. - 18 -C 2 H s ACH 3 C02CH3 XL N C 2 H 5 /,,. / H 3 T C02CH3 XLI hv hv 2 n5 #CH 3 ""C02CH3 -2n5 94% XLVII C2H5, CH3 H x* C02CH3 16% XXVI H ... C02CH3 V , JOA-. A 'iii C 2H 5* C02CH3 6% XXV Figure XXIII. Photolysis of cis- and trans-3-Methyl-4-ethyl-3-carbo-methoxy-A^pyrazolines. Compound Identification Most sample identifications were based on the physical data obtained from infrared, n.m.r. elemental microanalysis and gas chromatography. a. Infrared Spectra The cis-3-methyl-4-ethy1-3-carbomethoxy-A1-pyrazoline (XL) showed a carbonyl band at 1748 cm"\and the -N=N- band was at 1538 cm whereas the trans-3-methyl-4-ethy1-3-carbomethoxy-A1-pyrazoline (XLI) showed the carbonyl group band at 1742 cm - 1 and the -N=N- at 1529 cm Infrared spectra of methyl cis- and trans-2,3-dimethyl-2-pentenoate showed the carbonyl bands at 1718 cm 1712 cm consistent with the o t , B -unsaturated ester structure assigned and the carbon-carbon double bond at 1647 cm"1, 1631 cm 1 respectively. The two cyclopropane derivatives, c i s- and trans-l-methyl-2-ethyl-l-carbomethoxycyclopropanes (XLVI and XLVII) showed no carbon-carbon double bond adsorption bands and the carbonyl group appeared at 1721 cm 1 and 1730 cm 1 respectively. - 19 -b. N.M.R. Spectra A l l the n.m.r. spectra are shown in the Appendix. The n.m.r. spectral data of pyrazolines XL and XLI are summarized in the Table I. The spectra of the pyrazolines XL and XLI closely resemble the published spectra of Van Auken and Rinehart (11) for cis- and trans-3,4-dimethyl-3-carbomethoxy-A^pyrazolines (IX and X). The assignment made to the isomeric cis- and trans-3-methyl-4-ethyl-3-carbomethoxy-A1-pyrazolines (XL and XLI) were based on a consideration of the chemical shift of the H r i•. When H„ . is cis to the ester group, i t s L-4 C-4" ^ peak should be at lower f i e l d . The assignment of configuration to these pyrazolines could also be obtained from the photolysis results for which the products are the cyclopropane derivatives with retention of the geometry of the starting material. These w i l l be described in detail later. Geometric configuration assignment of two isomeric a,6-unsaturated olefins (X^v and XXv^) by n.m.r. was based on the position of the 6-methyl group peak. The group cis to the ester group is expected to be less shielded than that of the group trans (21). Data are summarized as in the Table II., The n.m.r. spectral data of two cyclopropanes (XLVI and XLVII) are summarized as in the Table III. Comparison of the n.m.r. spectra with those of cis- and trans-1,2-dimethyl-.l-earbomethoxycyclopropane (XVII and XVIII (11) show sufficient simi-la r i t i e s for structural assignments. Particularly a peak at 9.65T in XLVI corresponds to a peak at 9.8T in the cis-isomer (XVII).In addition Chiu (22 (a) and (b)) has worked on the pyrolysis at 2S8°C of both compounds XLVI and XLVII and found that trans- cyclopropane XLVII underwent ring opening to yield methyl cis- and trans-2-methyl-4-butenoate (LII and LI) while the cis-cyclopropane.(XLVI)..did not react. Since the ethyl group must be on the Compound TABLE I The n.m.r. Data of cis- and trans-3-Methyl-4-ethy1-3-carbomethoxy-A1-pyrazolines CH3 of C02CH3 CH3 CH3 of CH2 of at C-3 C 2H 5 C 2H 5 He* T Value Multiplicity . Coupling Constants in c~p.s.-. Unit Han HcJ C 2H 5 CH3 He 3 pC0 2CH 3 He He C2H5 1 CH3 Jw CO . 2 CH 3 Ha . f t v N N 6.29 s 6,33 s 8.74 s 8.44 ' 9.12 d.t.. 9.07 d.t. 8.77 m M 5.25 J H E H A = 17 6.04 HeH c_ 4 A 5.19 8.2 J ' = 7.9 H-aHC-4 H E H A = 48 -6.03 HeHa= 17 \"t-i = J Ha HC-4 Aj, u = 52 8.0 7.90 m J . =8 vie overlap s = singlet d.t. = distorted triplet q = quartet m = multiplet *H£ and CH2 of the ethyl group were not resolved. Lie in the region 8.0 - 9.0 T * See Figure XXVIII page 27. TABLE II The n.m.r. Data of Methyl c i s - and trans-2,3-Dimethyl-2-pentenoate Compound CH3 of C02CH3 CH 3 at , CT2 CH3 at C-3 CH2 of C 2H 5 x Value Multiplicity Coupling Constants in c.p.s. Unit CH3 of C 2H 5 CH3 CH3 S A C H 2n5 C02CH; 6.34 8.21 8.21 (overlap) u n r e s o l v e d 7.62 J . =7.5 vie 8.99 J . = 7.5 vie C 2H 5 CH3 CH3 v* *C02CH3 6.35 8.16 8.03 long distance coupling J *= 1 c.p.s. A= 81 c.p.s 7.87 J . = 7.5 vie A~ 66 c.p.s, 8.98 t J . =7.5 vie s = singlet q = quartet t = triplet TABLE I I I The n.m.r. Data of cis- and trans-l-Methyl-2-ethyl-1-carbomethoxycyclopropanes CH3 of CH3 CH3 of CH2 of ring C02CH3 at C-l C 2H 5 C 2H 5 hydrogens Compound T Values Multiplicity Coupling Constant in c.p.s. Unit C 2 H 5 \ CH 3 ^/Cc02CH3 6.40 s 8.76 s 8.98 d.t. J . = VIC 5 A = 19 8.66 o J . = vie c.p.s. 5 8.6-9.72 m C 2 H \ - -CH 3 /^COoCHo 6.40 s 8.74 s 9.11 t J . = VIC 7 A = 27 8.58 q J . = vie c.p.s. 7 8.9-9.28 m s = Singlet t = trip l e t o = overlap m = multiplet q = quartet - 23 -same side as the ester group for reaction to occur by the.six-membered intermediate XLIX as shown in the Figure XXIV the geometry is defined by this reaction. HMe Kc0 2Me Me XLVII CH3 CHMe \ ,6 OMe XLIX "v. C02CH3 C02CH3 LII LI Figure XXIV. Ring Opening of trans-1-Methy1-2-ethy1-carbomethoxy-cyclopropane. When the vicinal ester and alkyl groups are trans to each other the compounds are inert under the reaction conditions. The n.m.r. of the 6,y-unsaturated olefin, methyl 2-methyl-3-ethyl-3-butenoate (XLVIII) shows for the CH3 of ester group a singlet at 6.40x and for the CH3 at the C-2 position a doublet at 8.76T with a coupling constant of J v ^ c = 7.0 c.p.s. The hydrogen at C-2 is a quartet at 6.89T with a coupling constant of 7 c.p.s. The CH2 is at 5.11x with 1 c.p.s. splitting by long range coupling. The hydrogens on C-5 appears a tr i p l e t at 8.96x with a coupling constant of 7.4 c.p.s. This spectrum is in complete accord with the structure assigned. - 24 -III. DISCUSSION, The preferred conformation of the starting pyrazoline has in a previous case (12) been found important for the discussion of the reaction. Evaluation of the conformation of the two pyrazolines cis- and trans-3-methy1-4-ethy1-3-carbomethoxy-A ^ pyrazolines (XL and XLI) is therefore given below in some detail. Steric Conformation of Pyrazoline Rings It is suggested by a comparison to the structure of cyclopentene that the five member ring is not a planar and has conformation minima in the envelope form (23,24) as shown in the Figure XXV. Figure XXV. Conformation of Pyrazoline Ring. By considering the coupling between two C-4 hydrogens and one C-5 hydrogen and with reference to the Karplus equation (12,25) the angle between the plane of C-3, C-4, C-5 and C-3, N-2, N-l, C-5 can be estimated. For a number of pyrazolines which are expected to be predominantly folded in one direction. The angle was found to be 25° for the average conformation. The Karplus equation (25) is given as H, = 8.5 COS2<f> - 0.28 (c.p.s.) (0° .< <J> ^  90°) or J H H, = 9.5 COS2.). - 0.28 (c.p.s.) (90° * <|> < 180°). The term J„ „, is the coupling constant of two vicinal hydrogens. The angle $ is - 25 -the dihedral angle between these two hydrogens and a l l the numerals are constants. The conformational assignment to cis- and trans-3-methy1-4-ethyl-3-carbomethoxy-A1-pyrazolines (XL and XLI) has been derived below with the assumption that a l l projected geminal angles are 120°. The two hydrogens at the C-5 position of pyrazoline XL (and also for XLI) appear in the n.m.r. at the T values of 5.25 and 6.04. These differences are not expected to be due to the influence of the ester group at the C-3 position, since the two hydrogens at the C-5 position of 3-methyl-3-carbo-methoxy- A ^ pyrazoline have the same T value of 5.43 (26). Inversion of the ring in this case results in an averaging of the chemical shift for the pseudo axial and pseudo equatorial shifts of these hydrogens. Since in pyrazoline-XL (and XLI) the hydrogen/at the C-5 position are not equivalent, one folded conformation appears more favored than the other. Presumably the two hydrogens at the C-5 position are shielded differ-ently by the azo group.due to their different relative positions with that group. We can consider the two positions to be axial and equatorial (H & and He0 • The hydrogen H a is expected to receive more shielding than H g as shown in Figure XXVI, This is supported by the fact that the axial hydrogen in the cis-3, 5-di-(p-anisyl)-A 1,-pyrazoline(14) appears at 4.80T due to a greater shielding by the azo group than in trans-S^-difp-anisylJ - A^pyrazoline where the corr responding hydrogen appears at 4.25T as a result of averaging between the conformations in this molecule in which i t would alternate between axial and equatorial positions. - 26 -// -N Figure XXVI. Axial and Equatorial Hydrogens at the C-5 Position of the Pyrazoline Ring. The coupling constants found for pyrazoline XL are J„ H = 8.2 c.p.s, e C-4 and'J HaH, = 7.9 c.p.s. are given in the Table I (for pyrazoline XLI the cor-C-4 responding constants are ^ = "^ HaHc 4 = c-P> s O- The calculated coupling constants for angles of 26° and 146° using the Karplus equation (25) are 6.59 and 6.25 c.p.s. and for angles 27° and 147° are 6.47 and 6.40 c.p.s. The observed values are about 1.6 c.p.s. larger but of the same relative magnitude. This suggests that the dihedral angles of Hg-H^ ^  = 26° and H&-H^ ^  = 146° for pyrazoline XL and He-Hc_4 = 27° and Ha-H C-4 147° for pyrazoline XLI showing a preference to the conformation as shown in the Figure XXVII, H e H c Figure XXVII. Dihedral Angles of H e-H C 4 and Ha-Hc_4 of the Pyrazoline. - 27 -The relative position of the ethyl group to the groups on C-3 are assumed to be the same as that the olefin used to prepare the pyrazolines as discussed earlier giving the preferred conformations of the two pyrazolines XL and XLI to be as in the Figure XXVIII. XLI Figure XXVIII. Preferred Conformation of cis- and trans-3-Methyl-4-ethyl-3-carbomethoxy-A^pyrazolines. Similar evaluation of the degree of folding by applying the Karplus equation to three other pyrazolines IX, X and XV reported in the literature give the following results. C02CH3 CH3- ' c P - C 6 H 4 O C H CeH^OCrlVp 1 N' XV He H C-4 HaH For pyrazoline IX (11) the dihedral angles are calculated to be 9.0 c.p.s. and 6.0 c.p.s. (Karplus value for 16° = 7.6 c.p.s. and for 136° = 4.6 16° and H,-H • . = 136° based on the J u u C-4 He H c _ 4 C-4 c.p.s.). The observed values are about 1.4 c.p.s. larger but of the same - 28 -magnitude again. For the pyrazoline X (11), the dihedral angles are calculated to be ^ e"^Q_4 = 24° and Ha-H(-._^  = 144° based on the coupling constants of J u „ = 8.1 c.p.s. and J„ u = 7.3 c.p.s. (Karplus values for 24° = 6.8 He H C-4 Ha HC-4 c.p.s. and for 144° = 5.9 c.p.s.). The observed values are again about 1.4 c.p.s. larger. For pyrazoline XV (14), the dihedral angles are calculated to be HD-He:4= 40° and Hc-He. = 160° based on the J„ u . = 8.0 c.p.s. and Hb""e J„ „ = 11.5 c.p.s. (Karplus values for 40°=4.7 c.p.s. and for 160° = 8.1 3. 6 c.p.s.). This indicates that the bulky p-anisyl groups in this cis-3,5-relationship gives the largest degree of folding yet observed. Considerations of Possible Mechanism for the Pyrolysis Reaction The stereochemistry for the formation of a,8-unsaturated esters from pyrazolines XL and XLI suggests that the pyrolysis is taking place on the conformation with the C-4 hydrogen in the equatorial position. Since this is not the preferred conformation and since i t has the C-4 hydrogen in a position trans to the nitrogen to be lost i t suggests that a requirement of this reaction is that the nitrogen is lost on the side trans to the hydrogen which is migrating as shown in the Figure XXIX. C 2H 5 iCH 3 XLI-LIII '""V"1" ""C02CH3 ,C 2H 5C0 2CH 3 XLIV C02CH3 A H- \ N > ( " N C 2 H 5 LIV CH3 , XLV CH3 Figure XXIX. Transition States of a,6-Unsaturated Esters Formation. Consideration of this requirement may however explain the variation in olefin - 29 -yield for pyrazoline IX, X, XL and XLI. The pyrazoline IX which has the greatest tendency to folding to the conformation with the C-4 hydrogen equatorial (favorable for olefin reaction) gives the highest olefin yield (70 %) while the pyrazoline XLI with the lowest tendency to fold into the conformation with an equatorial C-4 hydrogen gives the lowest olefin yield (17 % ) . Application of this mechanism to the pyrolysis of a pyrazoline mixture reported earlier by McGreer (12) correctly predicts the structure of the olefin formed. A mixture of 90 % cis,trans-3,4,5-trimethyl-3-carbo-methoxy -A 1-pyrzoline (LV) and 10 % cis,cis-3,4,5-trimethyl-3-carbomethoxy-A^pyrazoline (LVI) gave 6 % methyl 2,3-dimethyl-2-pentenoate (XLV) as the only a,8-unsaturated olefin product as shown in the Figure XXX. ^CH 3 CH^ ^CH3 *'C02CH3 \ /"'C0 2CH 3 + C 2 H ^ C 0 2 C H 3 XLV LVI 10% 61% 32% 6% Figure XXX. Pyrolysis of cis,trans- and cis-cis-3,4,5-Trimethyl-3-carbomethqxy-A 1-pyrazolines. This olefin, which is only now positively identified through the isolation of its isomer in this work, would result from each of the pyrazolines by loss of nitrogen trans to the hydrogen at C-4;. Crawford and Mishra (13) proposed a mechanism for the pyrolysis of some alkyl - A^pyrazolines. The kinetic evidence showed that the formation of olefin and cyclopropane products occurred through the same intermediate which they have proposed to be a planar symmetric molecule (LIX) through - .30 -overlap of a pair of p-orbitals between the two carbons C-1 and C-3 as shown in Figure XXXI. H H Figure XXXI. Intermediate with a Pair of p-Orbitals. This intermediate (LIX) can easily yield cyclopropane and olefin products by a-bond formation or by hydrogen migration respectively and i t is predicted to yield cyclopropane through a conrotatory process (19). If we apply this mechanism to the pyrazolines XL and XLI presented in this thesis, the intermediate (LX) would result by loss of nitrogen from XL on the side trans to the hydrogen at the C-4 position and from XLI on the side cis to the hydrogen at the C-4 position (similar but opposite loss of nitrogen from XL and XLI w i l l give intermediate LXI) as shown in the Figure XXXII. Paths 1 and 3 are not favorable in comparison with the paths 2 and 4 due to the additional energy for conformational inversion. For the migration of hydrogen and olefin formation intermediate LX would be expected to give the trans-olefin (XXVI) and intermediate LXI would give the cis-olefin (XXV). The experimental results show that pyrazolines XL and XLI give olefins XXVI and XXV respectively. That pyrazoline XL should give only the inter-mediate via the less favored conformation is unexpected. This observation therefore makes application of Crawfords's mechanism to this system unlikely. - 31 -A l j LXI Figure XXXII. Cyclopropane Intermediates of Pyrolysis of cis- and trans-3-Methy1-4-ethyl-3-carbomethoxy-A^pyrazolines. In discussion of pyrolysis of pyrazolines, both of ionic (10,11) and diradical (15,16,18) mechanisms have been suggested. The ionic mechanism proposed (12) that the bond between N-l and C-3 of pyrazoline ring opened to give the diazonium betaine intermediate (LXII) and that bond C-3 and C-4 would be restricted in i t s rotation to some degree because ^erf^ the gauche interaction by the bulky groups as shown in the Figure XXXIII. - 32 -C 2H 5 H' CH3 " j ^ C02CH3 A — ~ < CH3 C02CH3 XL cis XLI trans LXII H C 2H 5 \ 0 CH3 C02CH3 LXIII Figure XXXIII. Ionic Mechamism for the Pyrolysis of 3-Methyl-4-ethyl-S-carbomethoxy-A^pyrazoline. Rotation in this way could explain the fact that the cyclopropane formation was not stereospecific for the present study. The possibility that an intermediate like LXII is involved in the ring closure is not supported by the fact that the partial pyrolysis of cisj-S.S-dimethyl-S-carbomethoxy-A^pyrazoline (XI) (12) gave none of the isomeric pyrazoline in the recovered unreacted pyrazoline and i t has been concluded that the loss of nitrogen from such a species must be faster than bond rotation. The ionic intermediate suggests a more polar transition state than starting material. The variation of rate for the pyrolysis of cis- and trans-3,5-dimethyl-3-carbomethoxy-A^pyrazolines (12) in a number of solvents indicated that in this case the intermediate is not more ionic than the starting material. The intermediate for pyrolysis of pyrazoline XI and XII is not expected to be ionic since a study of the rates of pyrolysis of a similar series earlier in this laboratory by N. W. K. Chiu (12) showed l i t t l e variation with dielectric constant of the solvents. Mechanism of the Photolysis Reaction Photolysis of cis- and trans-3-methyl-4-ethyl-3-carbomethoxy-A1-- 33 -pyrazolines (XL and XLI) gave as main products the cyclopropane derivative with retention of the geometry of the pyrazoline and as minor products the olefins corresponding to loss of CH2N2, methyl trans- and cis-2-methyl-2-pentenoate pentenoate (XXVI and XXV). The mechanism of photolysis is therefore con-siderably different from that of pyrolysis. Two possible transition states concerted (LXIV and LXV) have been suggested for giving these products by a molecular mechanism by Van Auken and Rinehart as shown in the Figure XXXIV. C 2H 5 C0 2CH 5 _ „ C02CH3 ; C H 3 > SCH3 LXIV LXV Figure XXXIV. Transition States of Photolysis. Conversion to a cyclopropane with the same stereochemistry as the original pyrazoline by photolysis is not always 100 % stereospecific although there is always a greater tendency than in the thermal reaction (pyrazoline XII gives about 70:30 ratio by photolysis with retention predominating while pyrolysis give 20:80 ratio for 3,S-dimethyl-S-carbomethoxy-A^pyrazoline^. concerted Although a melocular mechanism is s t i l l therefore suggested further factors must be evaluated. - 34 -IV. EXPERIMENTAL  Experimental Instruments and Procedures a. Nuclear Magnetic Resonance (n.m.r.) spectra were recorded on a Varian Associates Model A-60 spectrophotometer by Mrs. A. Brewster. Samples were dissolved in carbon tetrachloride (usually 20 % by volume and tetra-methylsilane was used as an internal standard). b. Infrared Spectra were run on a Perkin-Elmer Model 137 spectrophotometer with sodium chloride optics. c. Vapor phase chromatography was carried out using an Aerograph Model A-90-P. d. Elemental microanalysis were performed by A. Bernhardt (W. Germany) and P. Borda of the Chemistry Department, University of British Columbia. e. Boiling points given were determined on 10 yl samples by the inverted capillary method. Sample Preparation a. Preparation of N-Nitroso-N-methylurea. N-Nitroso-N-methylurea was prepared by the procedure given in Organic Synthesis (27). A yield of 106 g (67 %) was obtained. b. Preparation of N-Nitroso-N-ethylurea. N-Nitroso-N-ethylurea was prepared by the procedure worked out by N. Chiu (28). The method was adapted with some modification. A sample of 300 g (5 moles) of urea was dissolved in a solution of 123 g (1.5 moles) of ethylamine hydrochloride, mixed well with 300 ml of water and a few drops of concentrated hydrochloric dcid. The mixture was' boiled gently under reflux for four hours. After cooling to room tem-perature, 110 g (1.5 moles) of 98 % sodium n i t r i t e was added and the - 35 -mixture was divided into six equal portions. Each portion was chilled with ice and added to an ice-cold solution of 17 g. (0.17 mole) of concentrated H2S0^ in 110 g. of ice with s t i r r i n g at such a rate that the temperature remained below 5°C. The N-nitroso-N-ethylurea, which rose to the surface as pale yellow crystals, was collected on a f i l t e r and washed with ice-cold water and dried by suction t i l l constant weight. The yield was 87 g. (0.75 mole) or 50 % of the theoretical yield. Preparation of Diazomethane. Diazomethane was prepared also by the procedure given in Organic Synthesis (29). It was used in the ether solution without d i s t i l l a t i o n . Preparation of Diazoethane (30). A sample of 50 g. (0.285 mole) N-nitroso-N-ethylurea was added to a stirred ice-cold solution of 300 ml. of anhydrous ether and 125 ml. of 40 % KOH at such a rate that the reaction was under control and the reaction temperature was kept below 5°C. The orange colored diazoethane-ether solution was decanted from the aqueous layer, washed with: 100 ml. of ice-cold water and dried with anhydrous potassium hydroxide pellets for two hours. The yield was approximately 35-40 %. Preparation of cis-and trans-3,5-Dimethy1-3-carbomethoxy-A1-pyrazolines (XI and XII) (12). Methyl methacrylate (I) was added slowly to the diazoethane in the abso-lute ether until the solution was discolored. The ether was removed using a rotary evaporator. The crude product was d i s t i l l e d under a reduced pressure of 0.3 mm., b.p. 52°C. The n.m.r. spectrum showed that the cis and trans forms of XI and XII were presented in the proportions of 36 % and 64 % respectively (20). - 36 -TABLE IV Dis t i l l a t i o n Fractions in the Separation to Yield Methyl cis- and trans-2-Methy1-2-pentenoate (XXV and XXVI) Fraction No. Boiling Point °C Wt. Yield . g-Wt. % of Compd.XXV Wt. % of Compd. XXVI 1 132-135 0.4 - -2 135-139 8.01 trace -3 139-142 0.35 9 . -4 142-143.5 2.67 19 -5 143.5-145 2.86 24 -6 145-147 6.09 23 -7 147-148 5.47 16 -8 148-153 3.79 8 5 Residue 6.02 - 98 Total Wt. 35.66 Fraction No. Boiling Point °C Wt. Yield g. Wt. % of Compd. XXV Wt. % of Compd. XXVI 9 134-136 1.12 - -10 136-139 3.02 <1 -11 139-143 2.69 11 -12 143-144 2.38 21 -13 144-148 10.10 20 -14 148-153 5.02 7 -Residue 5.82 - 90 Total Wt. 30.15 - 37 -Liquid Phase Pyrolysis of S^-Dimethyl-S-carbomethoxy -A^pyrazoline (XXV) (20) Liquid phase pyrolysis under reflux at normal pressure started from 90°C and became vigorous at 120°C. Pyrolysis was continued until bubbles of nitrogen were no longer evolved. Five products have been identified pre-viously as cis-1,2-dimethyl-1-carbomethoxycyclopropane (VI, b.p. 1|5°C, 45 % ) , trans-1,2-dimethy1-1-carbomethoxycyc1opropane (VII, b.p. 136°C, 27 %),. methyl cis_-2-methyl-2-pentenoate (XIII, b.p. 143°C, 10 %) , methyl trans-2-methyl-2-pentenoate (XIV, b.p. 156°C, 15 %) and methyl l-methyl-2-pentenoate (XV, b.p. 139°C, 3 % ) . Separation of Methyl cis-and trans-2-Methyl-2-pentenoate A 73.42 g. sample from pyrolysis of cis- and trans-3,5-dimethyl-3-carbomethoxy-A^-pyrazoline (XLIII) was divided into two parts (38.8 g. and 34.6 g.) and d i s t i l l e d by means of a 24-inch annular Teflon spinning-band d i s t i l l a t i o n column with an automatic reflux-ratio controller at a reflux ratio 5:1. The results of the two dis t i l l a t i o n s are given in the Table IV. a. Separation of Methyl trans-2-methyl-2-pentenoate (XXVI). The residues from the two fractional d i s t i l l a t i o n s (11.8 g.) were combined and r e d i s t i l l e d to give the separation shown in the Table V. TABLE V Purification of trans-2-Methy1-2-pentenoate by D i s t i l l a t i o n Fraction Boiling Point °C Wt. Yield Wt. .% of Compound No. g. XXVI 15 147-156 1.73 63 16 157-158 8.38 >99 residue 1.02 Total Wt. 11.13 - 38 " b. Separation of Methyl cis-2-methy1-2-pentenoate (XXV). Fractions 4-7 and 12-14 were combined and were re d i s t i l l e d to give the results listed in the Table VI. TABLE VI Attempted Purification of cis-2-Methyl- 2-pentenoate by D i s t i l l a t i o n Fraction Boiling Point °C Wt. Yield Wt. % of Compound No. g- XXV 17 134-140 1.46 12 18 140-143 3.55 22 19 143-145 2.47 31 20 145-146 1.97 34 21 146-146.5 3.63 28 22 146.5 5.37 27 residue 1.23 Total Wt. 19.68 In order to obtain the cis-ester XXV pure, fractions 18-21 were separated further by vapor chromatography using a 10-ft. dinonyl phthalate column until the purity was greater than 99%. In this way 1.29 g. of pure methyl cis-2-methyl-2-pentenoate (XXV) was obtained. Preparation of cis- and trans-3-Methyl-4-ethyl-3-carbomethoxy-A1-pyrazolines  (XL and XLI). a. Preparation of cis-3-Methyl-4-ethvl-3-carbomethoxy-A1-pyrazoline (XL). Methyl trans-2-methyl-2-pentenoate (8.36 g.) was reacted with excess diazomethane solution over several days with fresh diazomethane solution being added every second day. The ether was removed on the rotary evaporator to give the crude pyrazoline (10.8 g.) corresponding to a crude yield of 97 %. - 39 -Attempts to d i s t i l l this product in the normal way were unsuccessful due to decomposition. The pyrazoline XXI was d i s t i l l e d by use of a bulb to bulb d i s t i l l a t i o n apparatus (as shown in the Figure XXXV) at a reduced pressure of 0.22 mm. and with the o i l bath temperature maintained between 70-75°C. The pure cis-3-me thy 1-4-ethyl-3-carbomethoxy-A ^pyrazoline (XXI) was obtained. Calc. for C 8H l t tN 20 2; C, 56.45; H, 8.29; N, 16.46. Found: C, 56.31; H, 8.17; b. Preparation of trans-3-Methy1-4-ethy1-3-carbomethoxy-A1-pyrazoline (XLI). By a procedure similar to that used in the preparation of the cis-isomer (XL) there was obtained 1.70 g. of crude trans-3-methy1-4-ethy1-3-carbomethoxy-A1-pyrazoline (XLI) corresponding to a crude yield of 99 %. The pyrazoline was d i s t i l l e d by means of the bulb to bulb d i s t i l l a t i o n apparatus under a reduced pressure of 0.1 mm. and with the o i l bath maintained at 75°C to give pure trans-3-methy1-4-ethyl-3-carbomethoxy-A1-pyrazoline (XLI). Calc. for CeHj^^Oj,: C, 56.45; H, 8.29; N, 16.46. Found C; 56.38; 21 H, 8.32; N, 16.41. n^ : 1.4535. The characterization of these pyrazolines is based on the n.m.r. and is given in the results section and the n.m.r. spectra are presented in the Appendix. N, 16.75. n 21 D 1.4565. ft. 7 o i l bath Figure XXXV. Bulb to Bulb D i s t i l l a t i o n Apparatus. - 40 -Pyrolysis and Photolysis of cis- and trans-3-Methyl-4-ethyl-3-carbomethoxy- A^pyrazplines (XL and XLI). A l l pyrolysis mixtures were analyzed by vapor chromatography using a 0.25-inch by 10-ft. dinonyl phthalate column at 143PC with a head pressure of 50 p.s.i. The chromatograms are given as obtained with each experiment and the retention times reported have been normalized to the above conditions. The components were separated where possible using a 10-ft. dinonyl phthalate column. When separation was not possible identification was based on the co^finjection of the unknown mixture with a known sample of the anticipated compounds• a. Liquid Phase Pyrolysis of cis-3-Methy1-4-ethyl-3-carbomethoxy-A1-pyrazoline (XL). Pyrolysis of 100 ul of the pyrazoline in the liquid phase was carried out by heating the sample in a tube in an o i l bath. Pyrolysis started at 105°C and became vigorous at 140°C. Heating was continued until there were no nitrogen bubbles evolved. The product distribution as determined by chromatogram is shown in Figure XXXVI. Peaks III and V were separated and identified. Peak V: Methyl trans-2,3-dimethyl-2-pentenoate (XLIV) showed a retention time of 30.3 minutes, b.p. 170°C and n^ 5: 1.4490. Calc. C 8H 1 1 +0 2: C, 67.57: H, 9.924. Found: C, 67.39; H, 9.90. Since the 6-methyl was found at lower f i e l d (8.03T ) than in the cis-ester (8.21T, see below) i t is assumed to be cis to the ester group. See appendix for the n.m.r. spectrum. Peak III: cis-l-Methyl-2-ethyl-l-carbomethoxycyclopropane (XLVI) showed a 25 retention time of 24.2 minutes, b.p. 165°C and n D : 1.4318. Calc. for C 8H l l +0 2: C, 67.5>7; H, 9.924. Found: C, 67.40; H, 10.02. The n.m.r. of the - .41 -cyclopropane ring hydrogens gave peaks in the region 8.6-9.72x (see the result part and appendix). A peak at 9.64x corresponds to one found in the cis-1,3-dimethyl-1-carbomethoxycyclopropane at 9.76x (11). Peak I was identified as by injection of a known sample obtaned by photolysis of trans-3-methy1-4-ethy1-3-carbomethoxy-A1-pyrazoline (XLI) w i l l be described later. Peak II: It is assigned by n.m.r. as methyl 2-methyl-3-ethyl-3-butenoate (XLVIII) b.p. 160°C See the n.m.r. data and spectrum in results part and appendix. Figure XXXVI. Vapor Chromatogram of the product from the Liquid Pyrolysis of cis-3-Methy1-4-ethy1-3-carbomethoxy-A^pyrazoline. b. Vapor Phase Pyrolysis of cis-3-Methy1-4-ethy1-3-carbomethoxy-A1-pyrazoline (XL). A sample of the pyrazoline was injected in the v.p.c. with a 10-ft. D.N.P. column at 160°C and with the temperature of injector at 290°C. The product distribution is shown in the Figure XXXVII. - 42 -•in) (18.5 min.) Figure XXXVII. Vapor Chromatogram of the Product from the Vapor Pyrolysis of cis-3-Methyl-4-ethyl-3-carbomethoxy-A 1-pyrazoline. c. Photolysis of cis-3-Methyl-4-ethyl-3-carbomethoxv-A1-pyrazoline (XL). A sample of 0.5 g. of pyrazoline in 25 ml. absolute ether was irradiated with a 450 W Hanovia lamp for 6 hours under reflux. The ether was removed using a rotary evaporator and the crude product analyzed by v.p.c. to give the chromatogram shown in Figure XXXVIII. (24.2 min) Figure XXXVIII. Vapor Chromatogram of the product from the photolysis of cis-3-Methy1-4-ethyl-3-carbomethoxy-A1-pyrazoline. - 43 -Peak III was isolated and shown by n.m.r. to be identical cis-l-methyl-2-ethyl-1-carbomethoxycyclopropane (XLV) isolated from the liquid phase pyrolysis. The small peak (retention time 21.2 minutes) which was 15.6 % was shown by n.m.r to be methyl trans-2-methyl-2-pentenoate (XXVI). This is the ester that was used to prepare the pyrazoline. d. Liquid Phase Pyrolysis of trans-3-Methyl-4-ethyl-3-carbomethoxy-A1-pyrazline (XLI). Liquid phase pyrolysis started at 105°C and became vigorous at 140°C. The product distribution as determined by v.p.c. was as given in Figure XXXIX. Figure XXXIX. Liquid Phase Pyrolysis of trans-3-Methyl-4-ethyl-3-carbomethoxy-A 1-pyrazoline. By reducing the attenuation a trace of methyl trans-2,3-dimethyl-2-pentenoate became apparent as shown in the Figure XL. - 44 -Figure XL. The Product Distribution of Thermal Pyrolysis of trans-3-Methyl-4-ethyl-3-carbomethoxy-A1-pyrazoline with Reduced Attenuation (see Figure XL). Peak IV: Methyl cis-2,3-dimethyl-2-pentenoate (XXVII) showed a retention time of 27.0 minutes. The n.m.r. data proved i t to be identical! with an earlier prepared sample (b.p. 163°C) (12). The n.m.r. position of 8.21T for the B -CH3 compared with 8.03x in the trans-isomer confirms this structure assignment. e. Vappr Phase Pyrolysis of trans^3-Methy1-4-ethyl-3-carbomethoxy-A1-pyrazoline (XLI). A sample of pyrazoline was injected in the v.p.c. with a 10-ft. D.N.P. column at 150°C and the injection was 330°C. The products distribution as shown in the Figure XLI. - 45 -IV (27.0 mln.)3ll (24.2 mi*) II 1 (17.0 min) (18.5 minj Figure XLI. Products Distribution of the Product from the Vapor Phase Pyrolysis of trans-3-Methy 1-4-ethyl-3-carbo;-methoxy -A 1-pyrazoline. f. Photolysis of trans-3-Methy1-4-ethy1-3-carbomethoxy-A^pyrazoline (XLI). The same procedure used for photolysis of cis-3-methyl-4-ethyl-3-carbomethoxy-A1-pyrazoline (XL). The products distribution are shown in the Figure XLII. (17.0 aitj) Figure XLII. Product Distribution of the Porduct from the Photolysis of trans-. 3-Methy 1-4-ethyl- 3-carbomethoxy-A ^ pyrazoline. - 46 " Peak 1: trans:-l-Methyl-2-ethyl-1-carbomethoxycyclopropane (XLVII) showed a 25 retention time of 1 7 . 0 minutes, b.p. 147-8°C and n D : 1 . 4 3 2 8 . Calc. C 8H 1 i + 0 2 : C, 6 7 . 5 7 ; H, 9 . 9 2 4 . Found: C, 6 7 . 7 2 ; H, 9 . 8 4 . The n.m.r showed the peaks of.cyclopropane ring hydrogens distributed over the region 8 . 9 -9 . 2 8 x (see the result part and appendix) with no peak near 9 . 7 x as found in the other isomer. The small peak (retention time 2 1 . 2 minutes, 1 5 . 6 % ) was shown by n.m.r. to be methyl cis-2-methyl-2-pentenoate (XXV). This is the ester that was used to prepare the pyrazoline. -47 -BIBLIOGRAPHY 1. E. Buchner, M. Fritsch, A. Papendieck and H. Witter, Ann., 273, 214 (1893). 2. K. Von Auwers and E. Cauer, Ann. ,. . 470, 284 (1929). 3. K. Von Auwers and F. Konig, Ann., 496, 252 (1932). 4. B. Eistert, "Newer Methods of Preparative Organic Chemistry", f i r s t American edition^ Interscience publishers, New York, 1948, pp.551-556. 5. L. J. Smith and K. L. Howard, J. Am. Chem. Soc, 65_, 159 (1943). 6.. W. M. Jones, J. Am. Chem. Soc, 81, 5155 (1959). 7. D. E. McGreer, W. Wai and G. Carmichael, Can. J. Chem., 313, 2410 (1960). 8. R. Huisgen, H. Stangl, H. J. Sturm and H. Wagenhofer, Angew. Chem., 73, 170 (1961). 9. R. Huisgen, Proc Chem. Soc.,.p. 357 (1961). 10. W. G. Young, L. J. Andrews, S. L. Lindenbaum and S. J. Cr i s t o l , J. Am. Chem. Soc, 66_, 810 (1944). 11. T. V. Van Auken and Kj. L. Rinehart, Jr., J. Am. Chem. Soc, 84_, 3736 (1962) 12. D. E. McGreer, N. W. K. Chiu, M. G. Vinje and K. C. K. Wong, Can. J. Chem., 43., 1407 (1965) . 13. R. J. Crawford and A. Mishra, J. Am. Chem. Soc, 87_, 3768 (1965). 14. C. G. Overberger, N. Weinshenker and J-P. Anselme, J. Am. Chem. Soc, 87_, 4119 (1965). 15. S. G. Beech, J. H. Turnbull and W. Wilson, J. Chem. Soc., 4086 (1952). 16. D. E. McGreer, Ph.D. Thesis, University of I l l i n o i s , 1959 p. 22. 17. W. I. Awad, S. M. Abdel, R. Omran and M. Sobhy, J. Org. Chem., 26_, 4126 (1961). 18. C. G. Overberger and J-P. Anselme, J. Am. Chem. Soc, 84_, 869 (1962). 19. R. Hoffman. Abstracts of the 151st. National Meeting of the American Chemical Society, Pittsburgh, Pa. March 1966. K. 109. 20. D. E. McGreer, P. Morris and G. Carmichael, Can. J. Chem. 41, 726 (1963). - 48 " 21. L. M. Jackman,"Nuclear Magnetic Resonance Spectroscopy",,2nd impression 1962. p.119. 22. a) N. W. K. Chiu and D. E. McGreer, Abstract, Twenty-First Annual North-west Regional Meeting of the American Chemical Society, June, 1966, P.51. b) N. W. K. Chiu and D. E. McGreer, private communication. 23. C. W. Beckett, N. K. Freeman, and K. S. Pitzer, J. Am. Chem. Soc, 70, 4227 (1948). 24. D. A. Usher, E. A. Dennis and F. H. Westheimer, J. Am. Chem. Soc, 87, 2320 (1965). 25. M. Karplus, J. Chem. Phys. 30, 11 (1959). 26. I. Masters, private communication. 27. A. H. Blatt, "Organic Syntheses" Collective Volume II, 1955. p.22. 28. N. W. K. Chiu, M.Sc. Thesis, University of British Columbia, 1964, ' p.41. 29. A. H. Blatt, "Organic Syntheses", Collective Volume III, 1955. p.22. 30. N. W. K. Chiu, M.Sc. Thesis, University of British Columbia, 1964, p. 42. - 49 -APPENDIX The n.m.r. spectrum of cis-3-Methy1-4-ethy1-3-carbomethoxy-A^pyrazolines. - 50 -The n.m.r. spectrum of trans-3-Methyl-4-ethyl-3-carbomethoxy-A 1-pyrazolines. - 51 -The n.m.r. spectrum of cis-2,3-Dimethyl-2-pentenoate. - 52 -The n.m.r. spectrum of trans-2,3-Dimethyl-2-pentenoate. - 53 -The n.m.r. spectrum of cis-l-Methyl-2-ethyl-carbomethoxy-cyclopropane. 54 -The n.m.r. spectrum of trans-1-Methy1-2-ethyl-l-carbomethoxy-cyclopropane. - 55 -The n.m.r. spectrum of Methyl 2-methyl-3-ethyl-3-butenoate. 

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