New Data on the Mechanism of the Perkow-Arbuzov Reaction

105 New Data on the Mechanism of the PerkowArbuzov Reaction L Á S Z L ÓΤŐΚΕ, IMRE PETNEHÁZY, and GYŐNGYI S Z A K Á L — Department of Organic Chemical Technology, Technical University Budapest, 1521 Budapest, Műegyetem, Hungary

Downloaded by UCSF LIB CKM RSCS MGMT on November 23, 2014 | http://pubs.acs.org Publication Date: November 11, 1981 | doi: 10.1021/bk-1981-0171.ch105

HARRY R. HUDSON and LUBA POWROZNYK — Department of Chemistry, The Polytechnic of North London, Holloway Road, London, N7 8DB, England CHRISTOPHER J. COOKSEY — Department of Chemistry, University College London, 20 Gordon Street, London WC1H ΟAJ, England

In spite of many previous studies on the mecha nisms by which trialkyl phosphites interact with αhalogenocarbonyl compounds, the reactive intermediates which lead to ketophosphonate (Arbuzov reaction) and to v i n y l phosphate (Perkow reaction) have i n no cases been clearly i d e n t i f i e d . It i s generally believed (1), however, that the Arbuzov product 4 results from initial attack by phosphorus at the α-carbon atom, whereas the Perkow product 7 i s formed by initial attack at the carbonyl carbon atom, followed by migra tion of phosphorus from carbon to oxygen (Scheme 1). Scheme 1

Recent kinetic studies, however, provide strong evidence for the involvement of a common f i r s t i n t e r mediate (2). We have now carried out crossover experiments i n which the reaction of trimethyl phosphite with a mix ture of differently substituted chloro- and bromoacetophenones (e.g. C6H5COCH2Cl and p-MeC6H4COCH2Br) af fords a mixture of products whose composition shows that halogen exchange has occurred. In other words, the ratio of Perkow to Arbuzov products i s that which would be expected if C H COCH Br and p-MeC^H^OCH^l were also present in tne reaction mixture ^5 mol% i n benzene, 8 mol% in chlorobenzene, 23 mol% in acetonitrile). 0097-615 6/81/0171-0513$05.00/0 © 1981 American Chemical Society 6

5

2

In Phosphorus Chemistry; Quin, L., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

514

PHOSPHORUS

CHEMISTRY

As d i r e c t h a l o g e n e x c h a n g e b e t w e e n t h e k e t o n e s was e x c l u d e d b y s e p a r a t e e x p e r i m e n t s t h e r e s u l t s a r e b e s t e x p l a i n e d by a s s u m i n g t h a t an i o n i c exchange r e a c t i o n o c c u r s , i n v o l v i n g h a l i d e i o n from a q u a s i p h o s p h o n i u m i n t e r m e d i a t e (Scheme 2 ) . Scheme C.H C0CH Br c


Ό

Ο

o

Ζ

+ Cl~

2

C H C0CH Cl + Br" χ

r

c

D

b

o

Ζ

C o n f i r m a t i o n o f t h i s e f f e c t was o b t a i n e d b y c a r r y i n g out experiments i n the presence o f added n u c l e o p h i l e s ( i n the form o f t r i e t h y l b e n z y l a m m o n i u m c h l o r i d e , o r t e t r ab u t y 1 ammonium b r o m i d e ) w h i c h m o d i f i e d b o t h t h e product r a t i o and the o v e r a l l r e a c t i o n r a t e . To o b t a i n more i n f o r m a t i o n on t h e n a t u r e o f t h e quasiphosphonium intermediates i n v o l v e d i n these s y s t e m s we h a v e s t u d i e d t h e r e a c t i o n s o f s t e r i c a l l y h i n d e r e d n e o p e n t y l e s t e r s b y means o f Ρ nmr s p e c t r o s c o p y . T r i n e o p e n t y l p h o s p h i t e and α - b r o m o a c e t o p h e n o n e gave r i s e t o a p e a k a t +41 ppm due t o t h e k e t o p h o s p h o n i u m i n t e r m e d i a t e 3 (R = M e ~ C C H ; R' = P h ; X = B r ) w i t h i n h a l f an.hour o f mixing the r e a c t a n t s i n acetone-d at 27 C ( Ρ nmr s h i f t s a r e r e l a t i v e t o 85% H - P O , d ô w n f i e l d p o s i t i v e ) . P e a k s due t o t h e k e t o p h o s p n o n a t e 4 +19 ppm a n d t h e v i n y l p h o s p h a t e 7 ( - 7 ppm) w e r e a l s o observed (compound 4 and 7 have s a t i s f a c t o r y e l e m e n t a l a n a l y s i s a n d s p e c t r o s c o p i c d a t a ). T h e c o n c e n t r a t i o n o f t h e i n t e r m e d i a t e r e a c h e d a maximum a f t e r a b o u t t w o h o u r s when i t was p r e c i p i t a t e d f r o m a c e t o n e s o l u t i o n by t h e a d d i t i o n o f a n h y d r o u s e t h e r t o g i v e w h i t e c r y s t a l s o f t r i n e o p e n t y l o x y (phenacy1)phosphonium b r o m i d e , i d e n t i f i e d b y e l e m e n t a l a n a l y s i s a n d nmr s p e c t r o s c o p y ( Ρ 6+41, i n C D C 1 ~ ) . When r e d i s s o l v e d i n a c e t o n e - d ^ , deuterochloroform, acetic acid, or acetic acid-acetone m i x t u r e s , the i n t e r m e d i a t e decomposed t o y i e l d k e t o p h o s p h o n a t e 4 b u t none o f t h e v i n y l p h o s p h a t e 6 ( P e r k o w p r o d u c t ) . N o r was t h e c o u r s e o f r e a c t i o n a f f e c t e d by the a d d i t i o n o f c h l o r i d e i o n o r o f α - c h l o r o acetophenone i n a c e t o n i t r i l e . A p r o p o s a l ( _3 ) t h a t v i n y l p h o s p h a t e m i g h t b e f o r med f r o m t h e k e t o p h o s p h o n i u m i n t e r m e d i a t e , a f t e r r e arrangement v i a a four-membered c y c l i c phosphorane 8 i s t h e r e f o r e e x c l u d e d by o u r r e s u l t s under t h e s e r e action conditions. 2

f i

(RO ) Ρ — Ç H ι

?

I,

ο — (i)—R' c

8


105.

TÔKE E T A L .

Mechanism

of

the

Perkow-Arbuzov

515

Reaction

We a l s o f o u n d t h a t t h e v i n y l p h o s p h a t e w a s t h e major r e a c t i o n product i n t h e i n i t i a l stages o ft h e r e a c t i o n o f t r i n e o p e n t y l p h o s p h i t e w i t h α-bromoacetophenone i n acetone-d , b u t t h a t t h e product ratio changed i n favour o f t h e ketophosphonate as t h e reac t i o n p r o c e e d e d . The r e s u l t s a r e c o n s i s t e n t w i t h ar e a c t i o n scheme i n w h i c h t h e k e t o p h o s p h o n i u m a n d v i n y l oxyphosphonium intermediates a r e formed by p a r a l l e l pathways, e i t h e r d i r e c t l y from t h e r e a c t a n t s , o f from a common f i r s t i n t e r m e d i a t e X a n d i n t h e l i g h t o f o u r p r e v i o u s k i n e t i c s t u d i e s (2) the latter i sindicated (Scheme 3 ) .


f i

Scheme 1

+ 2

>

3 3

r

4

6

* 7

X

It i sclear also that the vinyloxyphosphonium i n t e r m e d i a t e 6 i s much l e s s s t a b l e t h a n t h e k e t o p h o s p h o n i u m i n t e r m e d i a t e 3, a l t h o u g h t h i s d i f f e r e n c e m a y o n l y b e a p p a r e n t when t h e a l k o x y g r o u p (R ) i s s t e r i c a l l y hindered as i n t h e case o f neopentyl. Intermediates d e r i v e d from dineopentyl phenylphosphonite and from neopentyl diphenylphosphinite were f o u n d t o be c o n s i d e r a b l y more s t a b l e . R e a c t i o n w i t h α-bromoacetophenone gave t h e c o r r e s p o n d i n g A r b u z o v i n t e r m e d i a t e s 9, 1 0 a s c r y s t a l l i n e s o l i d s , t h e d i p h e n y l p h o s p h i n i t e d e r i v a t i v e 10 b e i n g sufficiently Phè ( O R ) C H C O P h 2

B r "

2

P h ^(0R)CH C0Ph B r "

9

10

P h P ( 0 R ) 0 C (:CH ) P h C l " 2

2

2

(R=Me CCH ) 3

2

11 s t a b l e f o r X-ray c r y s t a l s t r u c t u r e determination t o be c a r r i e d o u t . I n d e u t e r o c h l o r o f o r m a t 100 C ( s e a l e d t u b e ), t h e i n t e r m e d i a t e s w e r e a g a i n s h o w n t o d e c o m p o s e to yield..the corresponding Arbuzov products e x c l u s i v e ly, the Ρ n m r s i g n a l s f o r 9 (ô +6 7.1) a n d f o r 1 0 (6+68.3) b e i n g r e p l a c e d b y s i n g l e p e a k s a t +32.1 a n d +28.2 ppm, r e s p e c t i v e l y . T h e p r e s e n c e o f p h o s p h o r u s jbonded C H groups i n t h e p r o d u c t s was c o n f i r m e d b y H nmr s p e c t r o s c o p y ( J f o r P-CLL 1 5 - 2 0 H z ) ; s i g n a l s d u e to v i n y l protons were n o t d e t e c t a b l e . From neopentyl d i p h e n y l p h o s p h i n i t e we w e r e a l s o a b l e t o o b t a i n t h e f i r s t example o f a c r y s t a l l i n e Perkow i n t e r m e d i a t e 11 ( £ +55.9) b y r e a c t i o n w i t h α - c h l o r o a c e t o p h e n o n e i n c h l o r o f o r m . Although r a t h e r u n s t a b l e , i t c o u l d be s t o r e d a t 0°C a n d w a s shown t o decompose t o t h e c o r r e sponding v i n y l e s t e r (6+29.7) when d i s s o l v e d i n deute2


516

PHOSPHORUS CHEMISTRY

terochloform (t, c a . 40 m i n u t e s , a t r o o m temperature ) The p r e s e n c e o f v i n y l p r o t o n s i n t h e i n t e r m e d i a t e a n d i n i t s d e c o m p o s i t i o n p r o d u c t was i n d i c a t e d b y c o m p l e x m u l t i p l e t s i n t h e H n m r s p e c t r u m c e n t r e d a t 5.45 a n d 5.1 p p m , r e s p e c t i v e l y . By c a r r y i n g o u t t h e r e a c t i o n o f t r i n e o p e n t y l phosphite w i t h α-bromoacetophenone i n the presence o f a c e t i c a c i d (10% i n a c e t o n e - d ) we h a v e a l s o o b t a i n e d evidence f o r the t r a n s i e n t existence o f the v i n y l o x y p h o s p h o n i u m s p e c i e s . U n d e r t h e s e c o n d i t i o n s , we o b s e r v e d the., r a p i d a p p e a r a n c e o f t h r e e t r a n s i e n t i n t e r m e d i ates ( Ρ α+92, +40, a n d -7.3 p p m ) , a l t h o u g h v i n y l p h o s p h a t e was t h e a l m o s t e x c l u s i v e f i n a l p r o d u c t . T h e p e a k a t - 7 . 3 ppm d i s a p p e a r e d m o s t r a p i d l y , w i t h t h e s i m u l t a n e o u s development o f a c o r r e s p o n d i n g peak a t -7.2 ppm d u e t o v i n y l p h o s p h a t e , a n d i s tentatively assigned to the vinyloxyphosphonium bromide.-J. t i s known t h a t t e t r a a l k o x y p h o s p h o n i u m i o n s h a v e Ρ chemi c a l s h i f t s which a r e n o t f a r removed from t h o s e o f t h e c o r r e s p o n d i n g p h o s p h a t e e s t e r s ( £ ). The i d e n t i t i e s o f t h e p e a k s a t +40 a n d +92 ppm a r e u n c e r t a i n . One l i k e l y s p e c i e s t o b e p r e s e n t i n a c i d c o n d i t i o n s i s t h e p r o t o n a t e d f o r m o f t h e b e t a i n e 5. Such i n t e r m e d i a t e s a r e assumed t o be formed i n a c i d c o n d i t i o n s and t o give r i s e t o the formation o f a-hydroxyphosphonates, ( RO) P (O) C H X (R') OH (1 ). I t i s a l s o l i k e l y t h a t t h e b e t a i n e 5 i s t h e f i r s t common i n t e r m e d i a t e (scheme 3 ) i n t h e f o r m a t i o n o f A r b u z o v a n d Perkow p r o d u c t s , t h e s e b e i n g formed b y a 1 , 2 - m i g r a t i o n o f t h e p h o s p h i t e m o i e t y t o t h e α - c a r b o n atom o r t o o x y g e n , r e s p e c t i v e l y . We d e t e c t e d n o s i g n a l a t +13 ppm w h i c h would be e x p e c t e d i f t h e b r o m o ( t r i n e o p e n t y l o x y ) phosphonium i n t e r m e d i a t e h a d been formed, a l t h o u g h such i n t e r m e d i a t e s a r e known t o b e v e r y s h o r t - l i v e d N o r was t h e c o r r e s p o n d i n g p h o s p h o r o b r o m i d a t e d e t e c t e d a t -8.5ppm (D ·


g

2

Literature cited 1. Chopard,P.A.; C l a r k , V . M . ; Hudson,R.F. and K i r b y , A . Tetrahedron 1965, 21, 1961. 2. T o k e , L . ; Petneházy,I. and S z a k á l , G y . J.Chem.Soc.Res. (S) 1978, 155. 3. Marquading,D.; Ramirez,F.; U g i , I . and G i l l e s p i e , P . Angew.Chem.Int.Edn. 1973, 12, 91. 4. F i n l e y , J . H . ; Denney,D.Z. and Denney,D.B. J.Amer. Chem.Soc. 1969, 91, 5826. 5. M i c h a l s k i , J . ; Pakulski,M and Skowronska,A. J . C . S . Perkin I . 1980, 833. RECEIVED July 7, 1981.


New Data on the Mechanism of the Perkow-Arbuzov Reaction

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