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Oxygen transfer reaction from cyclic nitrones to triphenylphosphine Agolini, Franco 1962

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OXYGEN T R A N S F E R R E A C T I O N FROM C Y C L I C NITRONES  TO  TRIPHENYLPHOSPHINE  by FRANCO LAUREA  IN  UNIVERSITY  THESIS  A  AGOLINI CHEMISTRY  OF MODENA  SUBMITTED  IN  OF T H E R E Q U I R E M E N T S MASTER OF in  (1958)  PARTIAL  FULFILMENT  FOR T H E D E G R E E  OF  SCIENCE  the Department of CHEMISTRY  We  accept  required  this  thesis  as  conforming to  the  standard  T H E U N I V E R S I T Y OF B R I T I S H July, 1962.  COLUMBIA,  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 f o r reference and study.  I further agree that permission  for extensive copying of t h i s thesis f o r scholarly purposes may granted by the Head of my Department or by h i s  be  representatives.  It i s understood that copying or publication of t h i s thesis f o r f i n a n c i a l gain s h a l l not be allowed without my written permission.  Department of  C /  The University of B r i t i s h Columbia, Vancouver 8 , Canada. Date  fj*  •  ( (ii)  A B S T R A C T  The  compounds i n the series from triphenylphosphine  to triphenyTbismuthine were examined as acceptors i n oxygen transfer reactions involving the l - p y r r o l i n e - l - o x i d e s . Triphenylphosphine was found to o f f e r a useful route from the l - p y r r o l i n e - l - o x i d e s to the corresponding p y r r o l i n e s . The second part of t h i s work i s centred on the s t r u c t u r a l investigation of Sanno's "base (XV) ( l ) , obtained as a "by-product i n the reductive c y c l i z a t i o n of ethyl 2-acetyl-2-ethyl-U-methyl-3-nitromethyl valerate (ay - n i t r o ketone) and, formulated "by the author as having the A* -pyrroline structure; to "be a c y c l i c nitrone  t h i s compound has since "been found (XVI).  In the case of t h i s complex  nitrone, the oxygen transfer reaction to triphenylphosphine has "been successful, y i e l d i n g two isomeric A' -pyrrolines. The  i s o l a t i o n of a A -pyrroline structure i s confirmation of  the proposed c y c l i c nitrone and  (XVI) structure f o r Sanno's "base  •as t h i s provides a p r a c t i c a l application of this reaction i n s t r u c t u r a l work as well as showing that triphenylphosphine w i l l reduce N-oxides i n the presence of an ester group.  (i)  ACKNOWLEDGMENT  I would l i k e  t o e x p r e s s my deep a p p r e c i a t i o n  t o D r s . R. B o n n e t t a n d D. E. M c G r e e r f o r t h e i r constant work.  h e l p and encouragement d u r i n g  this  (iii)  CONTENTS Page: Acknowledgment  i  Abstract  i  Table of Contents  i  Table o f Figures PART I :  i  i  v 1  Introduction  PART I I :  i  R e s u l t s and D i s c u s s i o n  12  Introduction  17  R e s u l t s and D i s c u s s i o n  22  EXPERIMENTAL: I.  P r e p a r a t i o n of 2,i4.,i4.-trimethyl-l-pyrroline from 2 , U , U - t r i m e t h y l - l - p y r r o l i n e - l - o x i d e  II.  P y r o l y s i s of 5,5-dimethyl-l-pyrroline1-oxide  III.  IV. V.  VI. VII.  30  Preparation of 5,5-dimethyl-l-pyrroline from the corresponding n i t r o n e  31  Preparation of 3-methyl-l-nitro-2-butanol  32  Preparation of 2-acetoxy-3-methyl-lnitrobutene  32  P r e p a r a t i o n of 3-rnethyl-l-nitrobute>ne-2  33  Preparation of E t h y l 2-acetyl-2-ethylU-methyl-3-nitromethyl valerate  VIII.  29  Preparation of Ethyl  3*4-  U-ethyl-3-isopropyl-  5-methyl-l-pyrroline-l-oxide-l(--carboxylate  3h  (iv)  Page: IX.  P r e p a r a t i o n of E t h y l  k-ethyl-3-isopropyl  -5-methyl-l-pyrroline-U-carboxylate X.  XI. BIBLIOGRAPHY  36  Oxygen t r a n s f e r r e a c t i o n t o t r i p h e n y l phosphine  38  A n a l y s i s o f the components  39 hi  (v) TABLES AND FIGURES Page:  TABLE I  Oxygen t r a n s f e r from 2,l+,U-trimethyl1-pyrroline-l-oxide  FIGURE I  11+  Vapour phase chromatogram of the deoxygenation of Sanno's "base  28  1  INT  R ODD"  C T I 0 N  PART I  The  reduction  of l - p y r r o l i n e - l - o x i d e s ( c y c l i c  to the c o r r e s p o n d i n g p y r r o l i n e s has c a r r i e d out  i n two  ways:  previously  (2) "been  2,l+,I|.-trimethyl-l-pyrroline-  1-oxide, f o r example, on treatment with z i n c and gave a  6695  w h i l e a 15^  y i e l d of the y i e l d was  c h l o r o f o r m was  nitrone)  corresponding p y r r o l i n e  acetic acid picrate,  o b t a i n e d when sulphur d i o x i d e  in  the r e d u c i n g agent.  O'  As  the n i t r o n e s  r e p r e s e n t a r e a c t i v e 1,3-system (3)  because of the n e c e s s i t y  to stop the r e d u c t i o n  at  p y r r o l i n e stage, i n v e s t i g a t i o n s were c a r r i e d out  and  the to f i n d  a  s u i t a b l e r e d u c i n g agent, which would have to combine s e l e c t i v i t y , r a p i d i t y and  effectiveness.  T h i s agent has been sought among the d e r i v a t i v e s of group V, p a r t i c u l a r l y s i n c e  triphenyl triphenylphosphine  2  has "been used s u c c e s s f u l l y t o remove oxygen from many s u b s t r a t e s (k).  Although phosphorus f o l l o w s n i t r o g e n i n  Group V there i s very l i t t l e  resemblance between the organic  chemistry of these two elements.  These  dissimilarities  a r i s e because o f the lower e l e c t r o n e g a t i v i t y o f phosphorus which p e r m i t s s t r o n g e r bond f o r m a t i o n w i t h oxygen and halogens and because o f the g r e a t e r r e a c t i v i t y o f the unshared e l e c t r o n s on the t e r v a l e n t phosphorus, which r e s u l t s i n a s t r o n g e r tendency t o the quinquavalency ( 5 ) .  These are  the main d i f f e r e n c e s by which the o r g a n i c chemistry o f the phosphorus i s r i c h e r than that of the n i t r o g e n .  In a l l i t s  r e a c t i o n s the d r i v i n g f o r c e i s the tendency t o the quinquav a l e n c y , tendency that can be i l l u s t r a t e d through numerous examples as i n the Arbusov r e a c t i o n ( 6 ) , where  trialkyl  p h o s p h i t e s r e a c t w i t h halogen d e r i v a t i v e s to give  dialkyl-  alkyl-phosphonates and halogen d e r i v a t i v e s , a c c o r d i n g t o the scheme:  RO RO-  0 +  R'X RO  R  T h i s r e a c t i o n p r o v i d e s a u s e f u l route to prepare some a l k y l h a l i d e s which are not otherwise r e a d i l y Another example  accessible.  i s the M i c h e a l i s r e a c t i o n ( 7 ) where a l k a l i  3  m e t a l d e r i v a t i v e s of d i a l k y l p h o s p h i t e s r e a c t w i t h a l k y l h a l i d e s t o give d i a l k y l  alkylphosphonates:  That the "bond "between phosphorus and oxygen, which i s f o r m a l l y w r i t t e n as double "bond, does, i n f a c t , have a considerable  amount  o f double bond c h a r a c t e r  i t s d i p o l e moment, by to the c a r b o n y l  i t s s h o r t l e n g t h and by  i t s resemblance  group i n p r o d u c i n g o< -methylene r e a c t i v i t y .  F o r t h i s r e a s o n the bond i s the  i s shown by  probably b e t t e r represented  as  hybrid:  — P =0  All  <  -p —  *  o  the t e r v a l e n t phosphorus compounds are  to o x i d a t i o n ( 8 ) .  This  is particularly  which the phosphorus atom has  attached  susceptible  true of those i n to i t a l k y l groups  which, s i n c e they are e l e c t r o n r e p e l l i n g ,  increase  the  a l r e a d y h i g h e l e c t r o n d e n s i t y on the phosphorus atom. Triphenylphosphine  i s outstanding  d e r i v a t i v e s o f Group V.  among the t r i p h e n y l  A comparison of the  d i p o l e moments:  D i p o l e moments o f the t r i p h e n y l d e r i v a t i v e s Group V Ph,N  Ph,P  Ph,As  PkuSb  Ph,Bi  3 0.22  3 1.U5  3 1.07  3 0.57  3 0.00  D  shows t h a t a s t h e  D  D  D  s e r i e s i s d e s c e n d e d t h e d i p o l e moments  d e c r e a s e s t e a d i l y and a l s o decreases.  D  so  the  nucleophilic character  T h i s has b e e n o n c e e x p l a i n e d  g r o u n d s o f an i n c r e a s e i n c o n j u g a t i o n  (10)  (9)  on  the  that i s expected  p a s s i n g f r o m a t r i a n g u l a r p y r a m i d a r r a n g e m e n t as  i t is in  t r i p h e n y l p h o s p h i n e , where the p h o s p h o r u s i s l o c a t e d a t apex o f the p y r a m i d , t o the p l a n a r of  t r i a n g u l a r arrangement  triphenylbismuthine. H o w e v e r , on t h e  b a s i s of a study  o f t r i p h e n y l a r s i n e , C u l l e n (11) there  is little  o r no  t h e compounds Ph M }  has  o f the U.V.  spectrum  r e c e n t l y suggested  that  c o n j u g a t i o n o f the l o n e p a i r o f  a r s e n i c w i t h the phenyl for  the  g r o u p s and  t h a t the  (-here M = P , S b , B i ) ,  same i s t r u e as t h e i r  spectra  resemble that of t r i p h e n y l a r s i n e . A c u r r e n t i n t e r p r e t a t i o n is  t h a t as the s e r i e s i s descended the l o n e p a i r  a c q u i r e s more " s " c h a r a c t e r w h i c h l e a d s decrease i n b o t h the  d i p o l e moment a n d  character.  triphenylphosphine  Although  orbital  to a subsequent the n u c l e o p h i l i c reacts very  a t o r d i n a r y c o n d i t i o n s w i t h a t m o s p h e r i c o x y g e n (12), c a p a c i t y t o a b s t r a c t oxygen from those there  slowly its  s u b s t r a t e s where  i s a v a i l a b l e an o x y g e n atom w e a k l y b o n d e d i s v e r y  w e l l known.  The  r e a c t i o n of benzoyl  peroxide  with  tri-  5  p h e n y l p h o s p h i n e t o g i v e "benzoic p h o s p h i n e o x i d e was f i r s t Wilson  anhydride  and t r i p h e n y l -  d i s c o v e r e d b y C h a l l e n g e r and  (13):  0  0  O  C H , G 0 OCC.H,  0  * C.H.C-O-CC.H, - F\PO  6  L a t e r , S h o n b e r g r e p o r t e d t h a t d i b e n z o y l d i s u l f i d e was reduced i n s i m i l a r f a s h i o n t o dibenzoyl s u l f i d e R e c e n t l y , Horner and J u g e l e i t  (15) h a v e made a t h o r o u g h  of the r e a c t i o n o f s e v e r a l types substituted  (ll+).  of peroxides with  study  tri-  phosphines.  I n g e n e r a l , a l l t h e compounds i n v e s t i g a t e d r e a c t with triphenylphosphine and p u r i t y .  to give products  Hydrogen peroxide  i nvery high  yield  i sreduced r a p i d l y i n  e t h e r e a l s o l u t i o n to give water and triphenylphosphine n-Butyl hydroperoxide  r e a c t s w i t h strong exothermic  to give the corresponding  oxide.  reaction  a l c o h o l i n 9Cr% y i e l d a n d i n s i m i l a r  f a s h i o n t e t r a l i n a l c o h o l h a s b e e n o b t a i n e d i n 98% y i e l d t e t r a l i n hydroperoxide.  An o l e f i n i c hydroperoxide  was a l s o  r e d u c e d s e l e c t i v e l y w i t h no a f f e c t t o t h e d o u b l e b o n d . the  other hand, d i a l k y l p e r o x i d e s  resistant  On  very  t o r e d u c t i o n and o n l y i n the case o f t h e q u a l i t a t i v e  reduction o f d i e t h y l peroxide reported.  are i ngeneral  from  Horner claimed  t o d i e t h y l e t h e r has i t been  that d i - t - b u t y l peroxide  s e v e r a l h o u r s o f h e a t i n g a t 111-120° w i t h  after  triphenylphosphine  6 gave the corresponding ether:  P P hi  ( C H  A  )  C O O C ( C H , \  4  However, t h i s reaction has "been reinvestigated "by Walling  (16)  and i t has "been shown that the reaction goes "by a free r a d i c a l mechanism and triphenylphosphine does not p a r t i c i p a t e .  Horner  reported also the satisfactory reduction of ozonides; cyclohexane ozonide gave the corresponding dialdehyde i n 70% yield:  An endo peroxide (ascaridol) was reduced to the corresponding endo oxide:  +  CH  CH CH,  CH,  CHj  CH,  The reduction of acyl peroxides, peracids, peresters, proceeds  7  smoothly.  In general, a l l these reactions proceed r a p i d l y  at room temperature i n solvents such as pentane or ether. A free r a d i c a l mechanism for these reactions does not seem l i k e l y as (a) there i s no attack on the solvent (b) the products of the reaction do not correspond to those of the known r a d i c a l decomposition of peroxides (c) the reaction i s not prevented by the addition of r a d i c a l i n h i b i t o r s . Horner has suggested that the reaction proceeds by the formation of an i n i t i a l adduct between triphenylphosphine and the peroxide and then subsequent attack by triphenylphosphine on one oxygen with the formation of a phosphonium ion, which can then combine to give the product and triphenylphosphine oxide according to the scheme:  R O O R '  ROOR'  -. p p hj  •—  ^  RC?  0—R  'PPh  RO  ©  R'  e -*  ROR  + P PO hj  Ph PO 3  Since these reactions proceed rapidly i n non polar solvents conditions which are unfavourable for ionic reactions, Hoffmann ( 1 7 ) investigated the reaction to determine  how  free any formed ions were, i f indeed any ions were formed  8  at a l l .  He p o s t u l a t e d t h e f o r m a t i o n o f a n i o n - p a i r whose  r a t e o f c o l l a p s e depends t o a l a r g e degree on t h e p o l a r i t y of the s o l v e n t .  I n non-polar  solvents the collapse i s quite  r a p i d a s c o m p a r e d t o more p o l a r s o l v e n t s w h e r e t h i s i o n - p a i r i s " l o o s e " enough so t h a t a f o r e i g n i o n c a n i n t e r v e n e t o a l a r g e r degree and a l t e r The  the n a t u r e  of the products.  effectiveness of triphenylphosphine  r e d u c i n g a g e n t h a s a l s o "been t e s t e d o n t h o s e there  i s a n o x y g e n atom w e a k l y b o n d e d .  (h) r e a c t s i n h o t g l a c i a l a c e t i c trimethylamine  C H  3  e  ©  Trimethylamine  p. p  quantitatively  \ /  CH»  t h a t t h e ease o f removal o f the oxygen  f r o m t h e amine o x i d e s d e c r e a s e s Pyridine-N-oxide  w i t h t h e d i p o l e moment.  and q u i n o l i n e - N - o x i d e  are r e s i s t a n t ,  h o w e v e r , t h e y h a v e b e e n r e d u c e d (18) b y m i x i n g together  oxide  oxide:  y  I t has been observed  s u b s t r a t e s where  acid to give  and t r i p h e n y l p h o s p h i n e  *\  as a s e l e c t i v e  the reagents  i n a b s e n c e o f s o l v e n t a n d u s i n g a Wood's m e t a l  Ph,P  + PhjPO l\J  bath:  9  The  quantitative  reduction  was  effected  150°:  at  of  ®  azoxybenzene  Ph P  C H,N=NC,Hr  •  6  to  (19)  C H,N=l\IC H t  t  azobenzene  *  f  PK P0 5  0®  Iodosobenzene  was  reduced  C H,I0  K  6  No r e a c t i o n although and that  a deep  was  colour  presence  aromatic  of  base  to  >  P  iodobenzene  > QH,I  observed  with  developed  triphenylphosphine. nitro  to  give  a Po  +  4  nitro  compounds,  on m i x i n g  Recently  compounds  (20):  it  (21)  react  with  azoxybenzene  nitrobenzene has  been  reported  phosphine  96%  in  in  the  be  used  yield:  0°  *C H,N0, —  ^ H  6  0  The with  possibility success The  has  been  can  that not  reduction noted:  even be of  *  C H N = © t  f  triphenylphosphine  NC H e  might  f  disregarded. an  aldonitrone  (h)  and  oxazirans  (22)  10  o  0  R-N = CH-R'  P h  *  > R-N = CH-R  P  -  P^PO  ®  E t h y l e n e o x i d e s a r e more r e s i s t a n t , h o w e v e r , t h e y h a v e "been reduced  a t 1 5 0 ° t o the corresponding o l e f i n s  \ ;  / c  —  Triphenylphosphine  <  Pv>, P  \ >  — - — >  (k):  / =  -  <  P ^ P O  r e a c t s a t 1 5 0 ° i n o-xylene  with  N - s u b s t i t u t e d t r i c h l o r o a c e t a m i d e s t o g i v e the c o r r e s p o n d i n g v i n y l a m i n e i n good y i e l d ( 2 3 ) :  CI  CI  o  C  C  /  Cl  N  >  \  1  C =  /  E t h y l e n e and s u b s t i t u t e d e t h y l e n e carbonates triphenylphosphine the carbonate  used.  a  C  + Pu PO  \  react with  (21+) g i v i n g t h e o l e f i n c o r r e s p o n d i n g t o Ethylene carbonate  and t r i p h e n y l -  11  phosphine heated over the temperature  range 130-200° i n the  absence of solvent gave triphenylphosphine oxide i n 93$ y i e l d and the o l e f i n i n 68$  CH  t  CH,  0\  /  C=0  yield:  Ph.P  P P0 «• L0 hi  t  •  C H ^ C H ,  O  With higher molecular weight carbonates, phosphine oxidation and subsequent o l e f i n synthesis occur only i f a catalyst i s used.  Large ring carbonates do not react. The use of triphenylarsine as an oxygen acceptor has  not been so extensively investigated although the s a t i s factory reduction of acyl peroxides to the corresponding anhydrides has been reported (U).  No information appears  to be available concerning the a p p l i c a b i l i t y of triphenylstibine  and triphenylbismuthine as oxygen acceptors.  12  RESULTS AND DISCUSSION  PART I  A c o n v e n i e n t method h a s been sought f o r the r e d u c t i o n of n i t r o n e s aqueous o r a c i d i c give yield  to p y r r o l i n e s which would  avoid  c o n d i t i o n s and w h i c h , moreover,  the p r o d u c t d i r e c t l y under  conditions  a minimum o f s t r u c t u r a l c h a n g e s .  that  would could  Such a p r o c e s s  i s r e q u i r e d f o r example i n c a s e s where t h e p r o d u c t o f a preparative  sequence  i s the 1-pyrroline-l-oxide  w h i c h i t i s t h e n d e s i r e d t o make t h e p y r r o l i n e .  from Oxygen  t r a n s f e r f r o m n i t r o g e n t o compounds o f o t h e r e l e m e n t s o f Group V s u g g e s t e d  itself  since triphenylphosphine  as a p o t e n t i a l method, e s p e c i a l l y has been used s u c c e s s f u l l y t o  remove o x y g e n f r o m many s u b s t r a t e s .  0  The r e d u c t i o n o f a n  a l d o n i t r o n e h a s b e e n n o t e d b u t no i n f o r m a t i o n a p p e a r s t o be  a v a i l a b l e concerning the a p p l i c a b i l i t y o f the r e a c t i o n  to purely a l i p h a t i c n i t r o n e s , i n c l u d i n g the 1 - p y r r o l i n e 1-oxides. 2,4,^-trimethyl-l-pyrroline-l-oxide  ( I ) was  chosen  as a m o d e l compound a n d was f o u n d t o be r e d u c e d b y triphenylphosphine.  I n o r d e r t o determine the b e s t  c o n d i t i o n s f o r t h e r e d u c t i o n e x p e r i m e n t s were c a r r i e d o u t under  a variety of conditions.  I t was f o u n d t h a t t h e  r e a c t i o n d i d not proceed t o a u s e f u l degree  i n refluxing  13  benzene or t o l u e n e .  The r e a c t i o n o c c u r r e d r a p i d l y , when  the substances were heated  together with a f r e e  flame,  and the p r o d u c t , 2 , U , U - t r i m e t h y l - l - p y r r o l i n e ( I I ) was d i s t i l l e d d i r e c t l y from  CH.-  the r e a c t i o n m i x t u r e :  CH,  —I A  P PO hl  -CH,  I. II A s i m i l a r r e s u l t was o b t a i n e d with t r i p h e n y l a r s i n e .  With  t r i p h e n y l s t i b i n e and t r i p h e n y l b i s m u t h i n e , however, e x t e n s i v e decomposition was e v i d e n t , and i n the l a t t e r case the main product  i n the d i s t i l l a t e was benzene.  Triphenylphosphine  oxide was i s o l a t e d from the r e s i d u e thus c o n f i r m i n g that the r e a c t i o n i n v o l v e s oxygen t r a n s f e r t o phosphorus. The  r e s u l t s are summarized and some comparisons  drawn i n Table I .  These r e s u l t s were not s u r p r i s i n g ,  because i t was expected  t h a t as t h i s s e r i e s was descended  the d e c r e a s i n g s t a b i l i t y o f b6th the carbon-metal  bond  and metal-oxygen bond would i n t e r v e n e a t some stage and g i v e s i d e r e a c t i o n s which would make the r e a c t i o n u s e l e s s as a p r e p a r a t i v e method.  Ik  TABLE I  O x y g e n T r a n s f e r F r o m 2,U,1+-Trimethyl1-Pyrroline-l-Oxide.  Reagent  Reaction With CH,1 (25)  E f f e c t of Heating Alone *  Weight of Distillate (g)  % Yield  %  Yield of Picrate /  Ph P  Rapid  Refluxes  0.66  75  57  Ph As  Slow  Refluxes S l i g h t Decorap.  0.61  70  U2  Ph,Sfe  Nil  Decomp.  0.1k  #  Ph,Bi  Nil  Decamp.  1.6  #  3  3  5  * Under the r e a c t i o n  3k  Trace  conditions.  One-G-ram p o r t i o n s o f n i t r o n e h e a t e d w i t h a n e q u i m o l a r of the r e a g e n t .  amount  / Prepared i n moist ether. # D i s t i l l a t e e x t e n s i v e l y contaminated by decomposition o f t h e o r g a n o m e t a l l i c compounds.  products  15  I t was  found that when the n i t r o n e was  w i t h a f r e e flame f o r 10 minutes there was recovery  of unchanged s t a r t i n g m a t e r i a l .  exclude at once the p o s s i b i l i t y genation,  heated alone  a complete T h i s would  of a p y r o l y t i c deoxy-  a process which has been observed w i t h  certain (26):  amine oxides as f o r example K - m e t h y l p i p e f i d i n e - N - o x i d e  The  r e a c t i o n was  pyrroline-l-oxide to the  a l s o a p p l i e d to  (ill),  a c y c l i c aldonitrone.  c y c l i c ketonitrone,  In  contrast  I , which i s f a i r l y s t a b l e  heat, 5 , 5 - d i m e t h y l - l - p y r r o l i n e - l - o x i d e The  5,5-dimethyl-l-  decomposition i s attended by  is  to  thermolabile.  the development i n the  i n f r a r e d spectrum of a broad a b s o r p t i o n band i n the 1660  cm ' -  region.  T h i s has  l e d to the s u p p o s i t i o n  i s o m e r i z a t i o n to the corresponding the r e a c t i o n s  involved:  A CH  lactam may  be  that  one  of  16  However, the oxygen transfer reaction evidently proceeds more r a p i d l y than the isomerization, for the reaction gave a 65% y i e l d of the crude 5,5-dimethyl-l-pyrroline (39% y i e l d as the picrate) and triphenylphosphine (57%) was  i s o l a t e d from the  III  residue:  IV  oxide  (IV)  17  I N T R O D U C T I O N  PART I I Sanno ( l ) r e p o r t e d that  i n the c y c l i z a t i o n of  ethyl 2-acetyl-2-ethyl-U-methyl-3-nitromethyl valerate ( V ) , w i t h z i n c and a c e t i c a c i d , there was i s o l a t e d as a "byproduct a compound which he claimed to he the e t h y l U-ethyl-5-hydroxy-3-isopropyl-5-methyl-A -pyrrolineU-carboxylate ( V I ) :  C  ^  /  COOC»Hff N  CH  CH,2  o  CH,  3  n  /CHjCOOH  HO CH  NO,  V  VI  T h i s f o r m u l a t i o n may he q u e s t i o n e d o n t h e b a s i s o f t h e f o l l o w i n g more r e c e n t e x p e r i m e n t a l work. Of t h e f i v e p o s s i b l e s t r u c t u r e s  (VII-Xl) which can  be w r i t t e n f o r 2 - s u b s t i t u t e d p y r r o l i n e s o n l y A h a v e b e e n shown c o n c l u s i v e l y t o e x i s t :  a n d A*  18  H  H  H  VUI  VII  N' i  i  i  IX  T h e r e i s no c o n t r o v e r s y c o n c e r n i n g i d e n t i t y of A*-pyrrolines  (27).  t h e e x i s t e n c e and the  Compounds o f t h i s s t r u c -  t u r e a r e the u s u a l , h u t not t h e e x c l u s i v e (28, products pyrroles.  o b t a i n e d from the p a r t i a l r e d u c t i o n of s u b s t i t u t e d However, c o n f u s i o n has c e n t r e d around t h e  e x i s t e n c e o f A' - p y r r o l i n e s ( V I I a n d X I ) a n d ( V I I I and X ) .  38)  suggested e i t h e r the A  meric mixture  of t h e two.  r e c o n s i d e r e d r e c e n t l y (39  arbitrarily  compounds, w h i l e o r A*  Cloke  form or a t a u t o -  The q u e s t i o n h a s b e e n - U3),  and i n g e n e r a l t h e  c o n c l u s i o n has been drawn t h a t these predominantly  A*-pyrrolines  (30-36) h a v e  Several workers  assigned a A -structure to t h e i r (37,  29)  substances  exist  i n t h e A' - f o r m .  Both chemical adduced t o support determinations  (kh  and p h y s i c a l evidences this formulation.  t  s i g n i f i c a n t chemical  U3)  The Z e r e w i t i n o f f  have p r o b a b l y been the most  evidence  s i n c e t h e y h a v e shown t h a t  i n the examples s t u d i e d , l i t t l e was i m m e d i a t e l y  have b e e n  available.  o r no a c t i v e h y d r o g e n  P h y s i c a l evidence  b a s e d o n a number o f s t u d i e s o f u l t r a v i o l e t  has been  spectra  (U6),  19  but  t h e m o s t s i g n i f i c a n t r e s u l t s have come f r o m i n f r a r e d  studies  ( 3 9 , U l , 1+2, 1+1+).  h a v e shown l i t t l e  I n general, the p y r r o l i n e s  o r no a b s o r p t i o n i n t h e N-H s t r e t c h i n g  r e g i o n , b u t a strong band, a t t r i b u t e d to C = N i s present  i n t h e 1620-1650 cm"' r e g i o n .  absorption,  The s t r e n g t h o f  the C = N a b s o r p t i o n band, and e s p e c i a l l y t h e absence o f N-H a b s o r p t i o n a r e o f c o n s i d e r a b l e  importance.  I n the  l a t t e r a r e a d i f f i c u l t i e s have a r i s e n i n c e r t a i n i n s t a n c e s . T h u s , E v a n s (1+0) r e p o r t e d  that 2-methylpyrroline  weak b a n d a t 3.02yu , a n d B u r c k h a l t e r considered  (1+1)  and Short  a s i m i l a r b a n d a t 3 . 0 5 - 3 . 1 0 jx i n t h e s p e c t r u m  of 2-benzylpyrroline  t o b e a n o m a l o u s s i n c e t h e compound  d i d not c o n t a i n a c t i v e hydrogen. considered  showed a  O t h e r w o r k e r s have  t h a t " t h e N-H r e g i o n o f t h e i n f r a r e d a b s o r p t i o n  s p e c t r a o f p y r r o l i d i n e s and p y r r o l i n e s i s d i f f i c u l t t o interpret"  (1+1+, 1+7), a n d i t i s , o f c o u r s e ,  true  that  a b s o r p t i o n i n t h i s r e g i o n c o u l d be c a u s e d b y s p e c i e s , notably  traces of moisture  or o f dimer, other  than the  2 - p y r r o l i n e , w h i c h i s presumed t o be t a u t o m e r i c A' - f o r m .  w i t h the  F o r t u n a t e l y , proton magnetic resonance proved a  very useful tool.  B o n n e t t a n d M G r e e r (1+8) showed f o r C  a number o f c a s e s t h a t t h e p y r r o l i n e s i n q u e s t i o n d i d n o t give a s i g n a l i n the o l e f i n i c proton e  and  region  (2.0-5.5t)  t h i s was c o n s i s t e n t . w i t h o n l y t h a t s t r u c t u r e c o n t a i n i n g  the double bond i n t h e d - p o s i t i o n s i n c e a l l p o s s i b l e t a u t o r a e r s w o u l d have a t l e a s t one o l e f i n i c p r o t o n .  The  20  p r o t o n m a g n e t i c r e s o n a n c e s p e c t r a have s t r o n g l y r e i n f o r c e d previous  conclusions  the A - s t r u c t u r e of the  regarding  pyrrolines investigated. F u r t h e r m o r e , Bonnett and McGreer i n v e s t i g a t e d the p y r r o l i n e - l - o x i d e s , w h i c h a r e the f i r s t monomeric n o n aromatic  n i t r o n e s prepared  j»- n i t r o c a r b o n y l  compounds w i t h z i n c a n d ammonium  T o d d e t a l (2)  chloride.  Both chemical to support  (1+9) "by r e d u c t i o n o f  b y Todd  assigned  them t h e A" - s t r u c t u r e .  and p h y s i c a l evidences  this formulation.  have b e e n a d d u c e d  I n f a c t , t h e n i t r o n e s were  r e a d i l y reduced to c y c l i c secondary hydroxylamine by a q u e o u s KBH^;  by treatment  w i t h z i n c and a c e t i c a c i d  they  g a v e t h e A' - p y r r o l i n e , w h i l e w i t h t i n a n d h y d r o c h l o r i c a c i d t h e y gave t h e c o r r e s p o n d i n g s t r u c t u r e s were supported that these  y  The  by the p h y s i c a l p r o p e r t i e s  compounds showed a s i n g l e u l t r a v i o l e t  a b s o r p t i o n maximum a t 229-235 to theC  pyrrolidine.  (£ ~ 9 0 0 0 ) a t t r i b u t a b l e  = N - 0 chromophore and they  i n f r a r e d absorption, the frequency  exhibit strong  ranging  f r o m 1600 t o  1620 cm"' f o r t h o s e b e a r i n g a 2 - a l k y l s u b s t i t u e n t a n d f r o m 1570  t o 1590  present.  B o n n e t t and McGreer c o n f i r m e d  cm"' when no s u c h s u b s t i t u e n t s were  u s i n g N.M.R. m e t h o d s ; proton  the assignment  the l a c k o f s i g n a l i n the o l e f i n i c  r e g i o n i s c o n s i s t e n t o n l y w i t h s t r u c t u r e (XII)  1 c o n t a i n i n g t h e double bond i n the A - p o s i t i o n s i n c e i t s  21  isomer (XIII) would have an o l e f i n i c  N  N'  0  OH  XII  XIII  proton:  22  R E S U L T S AND D I S C U S S I O N  PART  II Sanno  C^H^NO^,  (l)  reported  formulated  as  the  preparation  XV,  by  the  of  a  following  CHj  cw p /  CH-I  \•CH,  N  I  XV  CH>  CH  CH,-  CH^hK  XIV  route:-  /  COOCiHs  H O J  CH,  compound  CH,  23 Much of the chemical evidence f o r this structure i s summarized i n the scheme I below:  CH,HO  y  CH,  I  H  <** LOO*** CH.  ^ CH,  l  0  I O =C I CH,  COCH,  SCHEME I Bonnett et a l ( 5 0 ) have proved that compound XV i s not a A' -pyrroline but i s instead the corresponding 1-pyrroline1-oxide (XVI): ^CH»  CH t  CHj-  XVI  2h  and have reinterpreted the reactions as indicated i n Scheme I I :  N  0"©  CH  CH,  CHy  C«i ooCi«* c  N  A  l"  I  O  COCH,  CHj,  SCHEME II  ^ ^CH,  CH,  O.c  3  25  The  r e s u l t s o b t a i n e d below s t r o n g l y r e i n f o r c e the  reached by The  Bonnett. suggestion  nitrone provided the  conclusion  t h a t t h e Sanno p r o d u c t  XV  was  a  an o p p o r t u n i t y f o r the a p p l i c a t i o n of  oxygen t r a n s f e r r e a c t i o n w i t h  Of p a r t i c u l a r i n t e r e s t was  triphenylphosphine.  the p o s s i b i l i t y t o i n v e s t i g a t e  t h e r e a c t i o n on a compound c o n t a i n i n g t h e e s t e r g r o u p . F o r p u r p o s e s o f c o m p a r i s o n t h e p y r r o l i n e was  prepared  by  Sanno's procedure ( l ) : CH,  CHj  c H  .CH  \  CH.  N  i  COOCj^S  1  CH \  CH.  CH  I  CH,-  CH, r u C  "  0  3  Since by  ordinary d i s t i l l a t i o n  eliminate was  the n i t r o n e p r e s e n t  i t was as  not p o s s i b l e  p u r i f i e d by vapor phase chromatography.  h5%,  the  The  i n f r a r e d s p e c t r a o f w h i c h showed  were c i s and  o f b o t h w e r e so s i m i l a r  chromato-  components i n r a t i o  trans isomers.  The  55  striking  s i m i l a r i t i e s e x c e p t i n the f i n g e r p r i n t r e g i o n , t h a t these  to  i m p u r i t y , the p y r r o l i n e  gram i n d i c a t e d t h e p r e s e n c e o f two to  N  / MO,  indicating  N.M.R. s p e c t r a  t h a t no f i r m c o n c l u s i o n c o u l d  be  e d r a w n as important  to the s t e r / o c h e m i s t r y o f e a c h i s o m e r . r e s u l t was  t h a t n e i t h e r of the  p o s s e s s e d a b s o r p t i o n i n the  The  components  o l e f i n i c proton  r e g i o n of  the  26  spectrum.  Since  a n a l y s i s of the p i c r a t e s i n d i c a t e d t h a t  t h e "bases were i s o m e r i c , t h e y a r e e v i d e n t l y t h e c i s t r a n s - 1 - p y r r o l i n e s , f o r which the a b s o l u t e is  still  and  stereochemistry  unknown:  (A CH,  CH,  XVII c i s and The  n i t r o n e XVI  trans U-ethyl-3-isopropyl-5-methyl-  (ethyl  1-pyrroline-l-oxide-U-carboxylate)  s u b j e c t e d to  the  d e o x y g e n a t i o n r e a c t i o n w i t h t r i p h e n y l p h o s p h i n e , and  the  product  o f t h e d i s t i l l a t i o n was  p u r i f i e d by v a p o r phase  chromatography,  Triphenylphosphine  in  The  the r e s i d u e .  ( s e e p.28)  s p e c t r a and  distillate  two  i d e n t i f i e d by  i t s i n f r a r e d a n d N.M.R.  ( X V I I I ) i n which the carboethoxy not p r e s e n t .  were decomposition oxygen-transfer the e x t e n t  products  The and  by  another  group at  other three were n o t  r e a c t i o n had  o f a b o u t 20$,  two  isomeric pyrrolines (XVII);  f r o m t h e a n a l y s i s o f i t s p i c r a t e t o be  p o s i t i o n k was  to  identified  i n d i c a t e d the p r e s e n c e of s i x components;  a t h i r d component was  The  o x i d e was  c h r o m a t o g r a m o f the  o f them were t h e e x p e c t e d  pyrroline  was  comppnents  identified.  e v i d e n t l y been accompanied,  a pyrolytic  ester  elimi-  27  nation,  f o l l o w e d by d e c a r b o x y l a t i o n ,  s u r p r i s i n g i n view of the high The  r e a c t i o n can be  a sequence  temperatures  summarized as  c«  A  CH l .C* / CH S  4  I  CH-  CH,  involved.  follows:  CHj c o o c ^  CH,  not  CH  2  V  'CH,  4  a po  CH.  CH,  fc  N  c i s and  trans XVIII  XVII  In order to prevent the p y r o l y s i s of the e s t e r , n i t r o n e was  treated with triphenylphosphine  benzene and  the mixture was  triphenylphosphine of n i t r o n e was  was  i n anhydrous  r e f l u x e d f o r 15 hours.  oxygen t r a n s f e r to triphenylphosphine r e c o v e r e d and  the  d i d not  occur  The since  a complete recovery  obtained.  These r e s u l t s show that Sanno's base i s a mixture of c i s and  trans forms (which have been i s o l a t e d and  characterized  at the p y r r o l i n e o x i d a t i o n l e v e l ) ,  s t r o n g l y support the view t h a t Sanno's base has nitrone  and  not  the  A  -pyrroline structure.  a l s o c o n s t i t u t e the f i r s t  a p p l i c a t i o n of the  t r a n s f e r r e a c t i o n t o s t r u c t u r a l work i n the  and the  They oxygen pyrroline  series. r  28  29  EXPERIMENTAL.  I.  Preparation  of  2,l+.U-trimethyl-l-pyrroline  from  2«UtU-trimethyl-l-pyrroline-l-oxide. T 2 .i+.if-^rimethyl-l-pyrroline-l-oxide by  the  procedure  (a)  of  Todd et  The n i t r o n e Eastman  Kodak  (free  flame)  volatile was  liquid  distilled  (0.66  a  for  infrared a band  present  in  together  C = N).  NO  The p i c r a t e ,  obtained  in  of  the  nitrone  m.p.  procedure two  the  the of  at  with  and (lit.  79°)  were  heated  apparatus. a  The  short  minutes  15  pressure,  time  and  then  110-130°  b.p.  (film)  3620  a  strong  b a n d was  found at  picrates  al  was  cm"  No  (Nujol mull)  since ,  1650cm  no = N -  in  w i t h an  infrared were  0).  ether,  depression  obtained by  The  to  band at  prepared  point  picrate (2).  basic  starting  present  1621  mixed melting  T o d d ejt  the  sharp  from ethanol.  pyrroline  of  cm"' a t t r i b u t e d  hygroscopic  195-196°,  and r e c r y s t a l l i z e d  the  about  spectrum  a b s o r p t i o n b a n d was  of  (m.p.  formed a f t e r  atmospheric  showed  material,  sample  mole)  mole)  distillation  which  prepared  75%).  g  moisture  (  (0.0078  g)  (0.0095  g)  gently  at  The liquid  (2.5  in  refluxed  (l  was  (2).  triphenylphosphine  79°) (51)  m.p.  (I)  al  (i)  was  authentic the spectrum  identical.  30  The residue (2.6 g) from the d i s t i l l a t i o n was extracted with cyclohexane and the solution treated with Norite.  On cooling, colorless needles were  formed and after c r y s t a l l i z a t i o n from cyclohexane (0.6 g 23$) triphenylphosphine oxide, m.p. was obtained ( l i t . m.p. (b)  156-158°  156°) (51).  In three t r i a l experiments the reaction was repeated as above, except that the phosphine  was  replaced by equimolar quantities of triphenylarsine, triphenylstibine and triphenylbismuthine (Eastman Kodak).  In the l a s t two cases decomposition  products from the organometallic compound were present i n the d i s t i l l a t e s .  The results of these  experiments are indicated i n Table I. II.  Pyrolysis of 5.5-dimethyl-l-pyrroline-l-oxide. 5,5-^imethyl-l-pyrroline-l-oxide was prepared by the  procedure of Todd et a l (2). A sample of 5,5-dimethyl-l-pyrroline-l-oxide  was  heated i n a closed f l a s k i n an o i l bath at 100° and the i n f r a r e d spectrum of the mixture was taken at i n t e r v a l s . During the course of 3 hours a peak at about 1660 very weak i n i t i a l l y ,  cm"',  increased s l i g h t l y i n i n t e n s i t y .  A f t e r a further hour at 180° the sample became very dark. The peak at 1660 cm  -1  had become very sharp and strong  31  whilst  the i n i t i a l  <s>  ©  p e a k o f t h e n i t r o n e a t 1575 cm  ( ) C = N - 0 ) was now a b s e n t .  Thermal p y r o l y s i s i s t h e r e f o r e  s l o w a t 100° b u t m e a s u r a b l e a t 180°.  The p y r o l y s i s p r o d u c t  was n o t i d e n t i f i e d . III.  Preparation the  of 5,5-dimethyl-l-pyrroline  corresponding  ( I V ) from  nitrone I I I .  5,5-^imethyl-l-pyrroline-l-oxide  ( I I I ) ( l g) ( 0 . 0 0 8 8  m o l e ) was t r e a t e d w i t h t r i p h e n y l p h o s p h i n e  (2.62 g) (0.01  m o l e ) as above, and t h e v o l a t i l e l i q u i d b o i l i n g  up t o 10k°  was c o l l e c t e d a s c r u d e 5 , 5 - d i m e t h y l - l - p y r r o l i n e ( I V ) (0.55  g 6 5 $ ) , t h e i n f r a r e d s p e c t r u m o f w h i c h showed a s h a r p  p e a k a t 1 6 1 8 cm"' ( C = N ) .  T h a t n i t r o n e b a n d was ©  -1  was shown b y t h e l a c k o f a b a n d a t 1 5 7 5 cm The  present ©  (^C = N - 0 ) .  y i e l d was n o t i m p r o v e d b y u s i n g a Wood's m e t a l b a t h  a t 300° i n p l a c e  of a f r e e flame.  A f t e r p u r i f i c a t i o n by  v a p o r p h a s e c h r o m a t o g r a p h y t h e p r o d u c t h a d t h e same i n f r a r e d s p e c t r u m as a s i m i l a r l y p u r i f i e d sample o f t h e a u t h e n t i c base prepared according The  p y r r o l i n e I V ( 0 . 3 7 g ) was t r e a t e d w i t h a  s o l u t i o n of p i c r i c (1.13 The  t o t h e p r o c e d u r e o f T o d d e_t a l ( 2 ) .  a c i d i n moist ether  t o give the p i c r a t e  g 3 7 % ) w h i c h was i d e n t i c a l w i t h a n a u t h e n t i c  residue  of methanol  saturated  ( 2 . 5 g ) was d i s s o l v e d i n a v e r y  small  sample. quantity  ( 5 m l ) a n d t h i s s o l u t i o n was p o u r e d o n t o a  column o f d r y alumina.  Elution with petrol-ether  (65-110°)  gave c o l o r l e s s n e e d l e s ,  w h i c h were c r y s t a l l i z e d f r o m c y c l o -  • 32  hexane to g i v e 1.52  g (57$)  of t r i p h e n y l p h o s p h i n e o x i d e ,  m.p.  156-158°.  IV.  P r e p a r a t i o n of 3 - m e t h y l - l - n i t r o - 2 - b u t a n o l . To a mixture of 100  11.h  g (1.63  mole) of nitromethane,  g (0.082 mole) of potassium carbonate and 70 ml of  water,  there was  added dropwise, w i t h s t i r r i n g at a  temperature kept below 50°  (the r e a c t i o n i s s l i g h t l y  exothermic - no h e a t i n g i s needed) 76 g (1.05 isobutyraldehyde.  As the r e a c t i o n proceeded the mixture  became red-orange. mixture was 2 hours.  mole) of  A f t e r the a d d i t i o n the r e a c t i o n  s t i r r e d a t room temperature f o r a f u r t h e r  Then i t was  c o o l e d i n an i c e b a t h and brought  to a ptf of 3 hy adding d i l u t e h y d r o c h l o r i c a c i d . r e s u l t i n g mixture was  The  e x t r a c t e d with e t h e r , washed w i t h  water, aqueous sodium b i c a r b o n a t e and a g a i n w i t h water. The e t h e r e a l e x t r a c t was  d r i e d over magnesium s u l f a t e , then  c o n c e n t r a t e d and d i s t i l l e d under reduced p r e s s u r e to give 105  g (80$)  (lit.  (52)  of the n i t r o a l c o h o l (b.p.g 7 2 - 7 U ° , n ^ b.p.g 7 2 - 7 U ° ) .  V.  cm ' -  (symmetric  1.104-62)  The product showed i n f r a r e d  bands at 3U72 cm""' (OH), 1560 1387  5  cm"'  (asymmetric N0 ) 2  and  N0 ). 2  P r e p a r a t i o n of 2-acetoxy-3-methyl-l-nitrobutane. To a s o l u t i o n of 100 g (0.75  mole) of the n i t r o -  a l c o h o l i n 65 ml of c h l o r o f o r m t h e r e was  added dropwise  33  with  stirring  acetyl the  at  chloride  room t e m p e r a t u r e dissolved  a d d i t i o n was  refluxed  for  solvent  was  distilled  product  completed,  2 hours  The  was  (b.p.  >  and  82-85°,  1.U3U5).  at  ( C = 0  1754 c m " '  1 3 8 1 cm""  VI.  Preparation  A mixture 69  g  (0.728  of  b e n z e n e were  more  water  refluxing The  give  b.p.^  3  of  off  g  (  oil  the  to  110 g of  anhydrous  After  the  (72.3%) The  C = C),  After was  overnight.  thus  (lit.  obtained  120 g  * . p .  (52)  of  (91%) .  2  5  s p e c t r u m showed bands  (asymmetric (  NOg),  C - 0 acetate  a procedure  group).  under  a water-trap  6 hours  oil of  of  the  infrared  and  the  to  1 3  acetate,  and 800 m l until  connected was  no  to  The  solvent reduced  66-67°)  were  was pressure  (lit.  s p e c t r u m showed bands and 1357 cm"'  the  completed.  sodium acetate  under  (b.p.  1538 cm" (NOg) 1  nitro  reflux  reaction  distilled  olefin  the  sodium carbonate  vigorously in  similar  (53).  (0.628 mole)  sodium carbonate  and  stand  give  a n d 1238 cm""  and Ross  collected  66-67°).  1650 cm"'  and  and washed w i t h b e n z e n e .  off  50  to  prepared by  stirred  flask.  distilled to  was  excess  filtered  mole)  mixture  allowed  infrared  of  chloroform.  1.4345)  5  mole)  3-methyl-l-nitrobutene-2.  Drake of  2  (0.75  reaction  1563 c m " ' 2  of  reported by  n  N0 )  T h e o l e f i n was that  off  The ),  (symmetric  1  the  of  reduced pressure  78-80°,  5  60 m l  then  distilled  under 0  in  g  59  (52) at  (NOg).  3k  Preparation of E t h y l 2-acetyl-2-ethyl-U-methyl-3-  VII.  nitromethyl valerate(V). 1-Ethylacetoacetic  a c i d e t h y l e s t e r was p r e p a r e d  a s i m i l a r procedure t o that reported by Robinson  by  (5U).  To a s o l u t i o n o f 76 g (C-.I4.8l m o l e ) o f 1 - e t h y l a c e t o a c e t i c a c i d e t h y l e s t e r i n l i i O m l a n h y d r o u s e t h e r a n d kO m l 2% N a O E t - E t O H t h e r e was a d d e d 3 6 . 5 g ( 0 . 3 8 5 m o l e ) o f 3-methyl-l-nitrobutene-2  i n 1+0 m l a n h y d r o u s e t h e r  w i t h s t i r r i n g a t room t e m p e r a t u r e . c o m p l e t e d t h e s o l u t i o n was s t i r r e d and  dropwise  A f t e r t h e a d d i t i o n was f o r a f u r t h e r 3 hours  t h e n a l l o w e d t o s t a n d a t room t e m p e r a t u r e f o r 2k  T h e n t h e s o l u t i o n was n e u t r a l i z e d w i t h a c e t i c a c i d , w i t h water and e x t r a c t e d w i t h e t h e r .  hours. diluted  The e t h e r e x t r a c t was  w a s h e d w i t h 8% s o d i u m b i c a r b o n a t e , w i t h w a t e r a n d t h e n d r i e d over magnesium s u l f a t e . vent,  t h e o i l was d i s t i l l e d u n d e r r e d u c e d p r e s s u r e  36 g (kl.6%) VIII.  A f t e r e v a p o r a t i o n o f the s o l -  of product  to give  b . p ^ 1 3 5 ° ( l i t . (52) b . p ^ 1 3 5 ° ) .  Preparation of Ethyl  k-ethyl-5-isopropyl-5-methyl-  1-pyrroline-l-oxide-U-carboxvlate. (XVI) To a m i x t u r e  o f 10 g ( 0 . 0 3 6 m o l e ) o f e t h y l 2 - a c e t y l -  2-ethyl-U-methyl-3-nitromethyl  v a l e r a t e , 2 g (0.373 mole)  o f ammonium c h l o r i d e i n 60 m l t e t r a h y d r o f u r a n a n d 20 m l o f w a t e r , t h e r e was a d d e d p o r t i o n w i s e 13.1+ with vigorous 25-30° .  s t i r r i n g while  g of zinc  t h e t e m p e r a t u r e was k e p t  dust between  A f t e r t h e a d d i t i o n was c o m p l e t e d t h e r e a c t i o n  mixture  was s t i r r e d f o r a f u r t h e r 3 h o u r s .  The s o l i d was  t h e n f i l t e r e d o f f a n d w a s h e d w i t h 60 m l o f h o t m e t h a n o l . The  f i l t r a t e was c o n c e n t r a t e d  and then d i s t r i b u t e d between  50 m l o f 5N h y d r o c h l o r i c a c i d a n d 50 m l o f e t h e r .  The e t h e r  l a y e r was d i s c a r d e d a n d t h e a q u e o u s l a y e r was made a l k a l i n e by  the a d d i t i o n o f potassium  was  e x t r a c t e d s e v e r a l times  dichloromethane  a Vigreux  The b a s i c  from the aqueous s o l u t i o n  ultraviolet  with  The s o l v e n t was d i s t i l l e d o f f a n d  o i l was d i s t i l l e d a t r e d u c e d p r e s s u r e  c o l u m n t o g i v e 5.5 g (63.7%) o f a v e r y  yellow-green  product  a n d t h e d i c h l o r o r a e t h a n e s o l u t i o n was d r i e d  over magnesium s u l p h a t e . the r e s i d u a l  hydroxide.  l i q u i d b . p . ^ 180-182°. a b s o r p t i o n (determined  #  The p r o d u c t  through  viscous showed  i n 95% e t h a n o l s o l u t i o n )  ©  ©  a t A max 237.5 (£ = 7935) ( ) C = N — 0 c h r o m o p h o r e ) a n d t h e i n f r a r e d spectrum o f the pure l i q u i d at  1 6 0 8 cm  ()C = N — 0 ) .  ( f i l m ) showed a b a n d  The N.M.R. s p e c t r u m d e t e r m i n e d  i n C C l ^ s h o w e d a q u a r t e t c e n t r e d a t 5 . 8 6 T (CHg i n COOCHgCH^) a n u n r e s o l v e d b r o a d b a n d i n t h e r e g i o n 8 t o 8.35 £(corresp o n d i n g t o 5 H ) , a t r i p l e t c e n t r e d a t 8.75s (CH^ and to  t w o s i n g l e t s a t 9.05 a n d 9.15?, a n d n o p e a k s  i n COOCHgCH^) attributable  o l e f i n i c h y d r o g e n atoms. The  picric  p i c r a t e was made f r o m a s a t u r a t e d s o l u t i o n o f  acid  i n ethanol and a f t e r c r y s t a l l i z a t i o n  from  e t h a n o l i t h a d m.p. 106-107° ( l i t . (52) m.p. 1 0 2 ° ) .  36  IX.  Preparation of Ethyl  U-ethyl-^-isopropyl-S-methyl-  1-pyrroline-ij— carboxylate. (XIV) To  a mixture  o f 17 g ( 0 . 0 6 2 m o l e ) o f e t h y l 2 - a c e t y l -  2-ethyl-4-methyl-3-nitromethyl  v a l e r a t e i n 90 m l o f a c e t i c  a c i d t h e r e was a d d e d p o r t i o n - w i s e 2 3 . 3 5 g z i n c d u s t vigorous After  s t i r r i n g while  t h e temperate was k e p t  with  a t 85-90°.  t h e a d d i t i o n was c o m p l e t e d t h e r e a c t i o n m i x t u r e was  stirred  f o r a f u r t h e r 2 hours on a steam b a t h .  T h e n i t was  p o u r e d i n t o h.00 m l o f c o o l w a t e r a n d n e u t r a l i z e d w i t h sodium hydroxide The 50  and e x t r a c t e d s e v e r a l times w i t h  e t h e r e x t r a c t was c o n c e n t r a t e d  ether.  and d i s t r i b u t e d between  m l 1 N h y d r o c h l o r i c a c i d a n d 50 m l o f e t h e r .  The e t h e r  l a y e r was d i s c a r d e d w h i l e t h e a q u e o u s l a y e r was made a l k a line  and then e x t r a c t e d w i t h e t h e r .  The e t h e r e x t r a c t was  d r i e d o v e r magnesium s u l f a t e and t h e n c o n c e n t r a t e d r e s i d u a l o i l w h i c h was d i s t i l l e d Two f r a c t i o n s were c o l l e c t e d ; at The  under reduced the f i r s t  to a  pressure.  one (6 g ) b o i l i n g  100-107°/3 mm a n d t h e s e c o n d one (2 g ) a t 178-183°/3 mm. i n f r a r e d spectrum o f the f i r s t  crude f r a c t i o n e x h i b i t s  a s t r o n g b a n d a t 16U7 cm"*' ( C = N) t o g e t h e r w i t h a s m a l l -I  although  s h a r p b a n d a t 1608 cm  0  ®v  ( C = N—0). N  The i n f r a r e d  s p e c t r u m o f t h e s e c o n d f r a c t i o n showed a s t r o n g b a n d a t 1608 cm"'.  Thus t h e f i r s t  f r a c t i o n was m a i n l y p y r r o l i n e  and  t h e s e c o n d f r a c t i o n was t h e 1 - o x i d e p r e p a r e d  above.  The  ultraviolet  (determined  in  spectrum of the second f r a c t i o n  95$ e t h a n o l s o l u t i o n ) showed a maxima a t 2 3 7 . 5 tyx.  37  U = 7935) (;c = N - 0 ) .  The p i c r a t e , m.p. 106-107°, o f  t h i s l a s t f r a c t i o n was made a s b e f o r e depression  f o r a mixture  a n d t h e r e was n o  m e l t i n g p o i n t w i t h the p i c r a t e  of e t h y l i + - e t h y l - 3 - i s o p r o p y l - 5 - m e t h y l - l - p y r r o l i n e - l - o x i d e l+-carboxylate. (determined olefinic  T h e N.M.R. o f t h e 1 - o x i d e  i n CCl^)  fraction  showed no a b s o r p t i o n a t t r i b u t a b l e t o  hydrogen.  The  first  f r a c t i o n was r e d i s t i l l e d  three  times, but  i t was n o t p o s s i b l e t o e l i m i n a t e t h e 1 - o x i d e i m p u r i t y . At t h i s stage,  a gas chromatogram through a 5 - f t Uconpolar  c o l u m n a t 175° w i t h a h e l i u m two by not  f l o w r a t e o f 67 c c . / m i n . g a v e  p e a k s a t 15, 16.3 m i n . i n r a t i o 55 t o hb%, d e t e r m i n e d t h e w e i g h t o f p a p e r c u t s o f t h e p e a k s ( t h e 1 - o x i d e was eluted a t t h i s temperature).  Separation  w i t h a p u r i t y o f 95 a n d 91% r e s p e c t i v e l y . spectra  ( f i l m s ) o f these  gave e a c h  The i n f r a r e d  two c o m p o n e n t s s h o w e d  b a n d s a t 1733 can"' ( C = 0) a n d a t 1647 cm"'  absorption  ( C = N) common  to  b o t h o f them b u t i t r e v e a l e d a l s o s i g n i f i c a n t d i f f e r e n c e s  in  the f i n g e r p r i n t region:  thus, the f i r s t  component h a d  a b s o r p t i o n b a n d s a t 1309. 111+2 a n d 971 cm"' w h i c h w e r e n o t present  i n the spectrum o f the second base.  b a n d a t 1608 cm""' was now a b s e n t . the  The 1 - o x i d e  I t i s thus apparant  two components a r e i s o m e r i c p y r r o l i n e s .  The N.M.R.  s p e c t r u m d e t e r m i n e d i n C C l ^ showed f o r t h e f i r s t a q u a r t e t c e n t r e d a t 5.85 ? ( C H unresolved  2  that  component  i n -COOCHgCH^), a n  b r o a d b a n d b e t w e e n 7.8 a n d 8.5^ ( c o r r e s p o n d i n g  38  to  a t 8 . 7 5 ? ( C H , i n COOCH_CEL) a n d two  5 H), a t r i p l e t  3  s i n g l e t s a t 9 . 0 5 ? a n d 9.15 2" .  c.  3  The N.M.R. f o r t h e s e c o n d  component showed a q u a r t e t c e n t r e d a t 5 . 8 5 t ( C H in-COOCHgCH^) 2  a n u n r e s o l v e d "broad h a n d a t 7 . 8 a n d 8 . 5 ? ( c o r r e s p o n d i n g t o 5 H), a triplet at  a t 8.75 T (CH^ i n -COOCHgCH^) a n d two s i n g l e t s  9 . 0 5 2" a n d 9 . 1 5 ? a n d no a b s o r p t i o n a t t r i b u t a b l e  hydrogen.  I t was c o n c l u d e d t h a t t h e s e two c o m p o n e n t s a r e Wa s  -the  cis  to o l e f i n i c  and t r a n s isomers b u t a b s o l u t e geometry^not A  The p i c r a t e  of the f i r s t  a saturated solution of p i c r i c  determined.  component was p r e p a r e d f r o m a c i d i n e t h a n o l a n d was  r e c r y s t a l l i z e d t h r e e t i m e s , m.p. 1 5 9 - 1 6 1 ° .  The i n f r a r e d  s p e c t r u m o f t h e p i c r a t e ( N u j o l m u l l ) showed b a n d s a t 1629 cm"' ( C = N ) , 1695 cm"' ( ) C = N - H) a n d a t 1745 cm"' 1  ( C = 0). Anal.-Calcd. C ^ H g g N ^  : C, 5 0 . 2 1 ; H, 5 . 7 7 ;  N, 1 2 . 3 3 .  P o u n d : C, 5 0 . 3 2 ; H, 5 . 8 4 ; N, 1 2 . 4 2 . The p i c r a t e o f t h e s e c o n d f r a c t i o n was p r e p a r e d i n a s i m i l a r m a n n e r , m.p. 1 5 0 - 1 5 1 ° .  The i n f r a r e d  spectrum  ( N u ^ o l m u l l ) was s i m i l a r w i t h t h a t o f t h e f i r s t O-f -tKe « pierrs.-te5  component.  s o r t e r \ C  The m i x e d m e l t i n g p o i n t ^ w a s 1 4 8 - 1 4 9 ° A n a l . - P o u n d : C, 5 0 . 2 0 ; X.  ( l i t . ( l ) m.p. 144 )  H , 5 . 8 4 ; N, 1 2 . 4 0 .  Oxygen t r a n s f e r r e a c t i o n t o t r i p h e n y l p h o s p h i n e . Ethyl-3-isopropyl-4-ethyl-5-methyl-l-pyrroline-l-  oxide-4-carboxylate phosphine  (1.3  ( l g) (0.00415 mole) a n d t r i p h e n y l -  g ) ( 0 . 0 0 4 7 5 m o l e ) were h e a t e d ( f r e e  flame)  39  i n a d i s t i l l a t i o n apparatus. 10 m i n u t e s .  The m i x t u r e "became d a r k  I t was r e f l u x e d f o r 15 m i n u t e s  t o g i v e 0.1+66 g b.p.  81+-180 , o f p r o d u c t . 0  and then  after distilled,  S i x components  were i d e n t i f i e d b y vapor chromatography  of this  product  u s i n g a 5 - f t U c o n p o l a r c o l u m n a t 170°.  The p e r c e n t a g e o f  t h e t o t a l p r o d u c t s was d e t e r m i n e d b y t h e w e i g h t s o f p a p e r cuts o f the peaks. phosphine  The r e s i d u e (1.1+ g ) f r o m t h e t r i p h e n y l -  r e a c t i o n was d i s s o l v e d i n c y c l o h e x a n e , h e a t e d  w i t h N o r i t e and gave,  o n c o o l i n g , 0.58 g (1+2.31+$) o f  t r i p h e n y l p h o s p h i n e o x i d e m.p. 156-158° ( l i t .  XI.  A n a l y s i s o f the v o l a t i l e I s o l a t i o n of the f i r s t  ( 5 1 ) m.p. 1 5 6 ° ) .  components. component (19.6$ o f t h e t o t a l )  g a v e a compound w h i c h was shown b y c h r o m a t o g r a p h y  t o have  a p u r i t y o f 97$.'  The i n f r a r e d s p e c t r u m showed a s t r o n g  p e a k a t 161+7 c m  ( C = N) a n d no a b s o r p t i o n i n t h e  - 1  carbonyl region.  The N.M.R. s p e c t r u m  d i d n o t have a s i g n a l  (determined i n CCl^)  i n the o l e f i n i c p r o t o n r e g i o n and  the q u a r t e t and t h e t r i p l e t  o f t h e CR" a n d CH^ o f t h e  c a r b o e t h o x y group were n o t p r e s e n t .  2  I t i s apparant  e s t e r p y r o l y s i s and d e c a r b o x y l a t i o n has o c c u r r e d .  that The  p i c r a t e was made i n t h e u s u a l m a n n e r , m.p. 128-129°. The  i n f r a r e d spectrum o f the p i c r a t e  ( N u j o l m u l l ) showed  b a n d s a t I63I+ cm"' ( C = N) a n d 1681+ cm"' ( ) C = I - H ) . Anal.-Calcd.  C-^H^N^O-, : C,50.21+; H,5.80; N,ll+.65.  P o u n d : C,50.2i+; H,5.75;  N,ll+.60.  ho  The  chromatogr.am gave  components 17.9.  in  These  the  following  three  purity  components  obtained  N.M.R.  identical the  for  zinc  with dust  the  following  ratio: he  two  isomeric  and a c e t i c  acid  i n m.p.  of  valerate.  pyrrolines  prepared by  synthesis.  the  ratio:  their  two  infrared  to  isolated ethyl The  in  two  and found  reduction  when m i x e d w i t h  last  of  pyrrolines  fourth  10.5-10.5-  percentage  159-161° and 150-151° r e s p e c t i v e l y )  depression  and  isolated  The  and p i c r a t e s ,  2-ethyl-U-methyl-3-nitromethyl (m.p.  third  i d e n t i f i e d b y means  spectra the  percentage  identification.  in  and 1 8 . 1 6 were  spectra,  second,  components c o u l d not  sufficient  23.27  the  be from  2-acetyl-  picrates  showed  no  corresponding  hi  BIBLIOGRAPHY  1.  Y. S a n n o , Y a k u g a k u  2.  R. B o n n e t t , R.F. C. B r o w n , V.M. C l a r k , I.O. 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