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A B S T R A C T
PART I
A STUDY OF MECHANISTIC VARIATIONS IN THE BROMINATION AND CHLORIN- ATION OF SOME ALKYL PHENOLS, PHENYL ETHERS AND PNENYL ESTERS.
The b r o m i n a t i o n s o f some 2 , 6 - d i a l k y l p h e n y l a c e t a t e s i n n i t r o - m e t h a n e a n d i n a c e t i c a c i d h a v e b e e n shown t o g i v e ( a ) p r o d u c t s o f s u b s t i t u t i o n a t b o t h t h e C - 3 and C-4 n u c l e a r s i t e s ( b ) p r o d - u c t s o f s u b s t i t u t i o n w i t h r e a r r a n g e m e n t l e a d i n g t o t h e f o r m a t i o n of v a r i o u s brom'nated a l k y L p h e n o l s a n d ( c ) u n i q u e l y i n a c e t i c a c i d , a p r o d u c t o f a l k y l s i d e - c h a i n s u b s t i t u t i o n . The b r o m i n a t i o n of t h e c o r r e s p o n d i n g b e n z o a t e d e r i v a t i v e s r e a l i s e d o n l y t h e p r o d - u c t s o f 3- s u b s t i t u t i o n . V a r i o u s p r o d u c t s o f ( a ) s u b s t i t u t i o n a n d ( b ) s u b s t i t u t j . o n w i t h r e a r r a n g e m e n t were d e t e r m i n e d i n t h e b r o m i n a t i o n o f 3 , 4 - d i m e t h y l p h e n y l a c e t a t e , p h e n y l a c e t a t e , a n d 2,3,5,6-tetramethylphenyl a c e t a t e . The b r o m i n a t i o n of 2 , 4 , 6 - d i m e t h y l p h e n y l m e t h y l e t h e r g a v e o n l y t h e e x p e c t e d p r o d u c t o f
n u c l e a r s u b s t i t u t i o n . E v i d e n c e f o r t h e l i k e l y i n v o l v e m e n t o f a d d i t - i o n - e l i m i n a t i o n s e q u e n c e s i n t h e f o r m a t i o n o f p r o d u c t s o f s u b s t i - t u t i o n w i t h r e a r r a n g e m e n t , h a s b e e n a d d u c e d . The p o s s i b l e r o l e o f v a r i o u s o t h e r p r o c e s s e s l e a d i n g t o t h e f o r m a t i o n o f d e a c y l a t e d p r o d u c t s i s d i s c u s s e d .
The c h l o r i n a t i o n o f 2 , 6 - d i m e t h y l p h e n y l a c e t a t e , 2 , 6 - d i m e t h y l -
p h e n y l b e n z o a t e a n d o f 2,3,5,6-tetramethylphenyl a c e t a t e i n b o t h
I
L I
acetic acid and nitromethane gave only.the expected product of nuclear substitution. The reaction of chlorine with 3,4-dimethyl- phenol, its acetate and methyl ether in acetic acid led to the formation of certain enone and dienone adduct derivatives which could be shown to rearrange under the conditions of the reaction to give (a) in the case of the phenol-products of substitution
and ( b ) for the acetate and methyl ether derivatives, products of
I
I substitution with rearrangement. The structures of the intermedi- ates were determi-ned from their spectral properties. Various
mechanisms likely to be involved in processes of chloro-deacylation and of chloro-demethylation are discussed; a consideration of cer- tain structural features of the substrates studied led to the con- clusion that chloro-deacylation and chloro-demethylation were
essentially processes initiated by ortho- attack of the chlorine molecule.
PART I1
REACTION PATHS IN THE BROMINATION OF CHOLEST-4-EM-3-ONE, CHOLEST- 5-EN-3-ONE AND 3-ACETOXYCHOLESTA-3,s-DIENE
The bromination of cholest-4-en-3-one can occur by a number of reaction paths. Conditions have been established under which react- ion can be established as occurring in part by electrophilic attack on (a) 3-hydroxycholesta-4,6-diene (b) 3-hydroxycholesta-2,4-diene
.. -
or its anion and (c) cholest-4-en-3-one; among the products can be included 2a-, 4-, 6B-, and 6a-bromocholest-4-en-3-one; 2a,6B-, 2a,6a-, and 4,6B-dibromocholest-4-en-3-one; and 2a,4,6B-tribromo- cholest-4-en-3-one. Unstable adducts involving the 4,5-double bond are implicated in a number of cases. The bromination of
cholest-5-en-3-one is equally complicated, and can involve addition to the 5,6-double bond,
Knowledge of the range of conditions and reagents through which 3-acetoxycholesta-3,5-diene is brominated to give 66-bromo- cholest-4-en-3-one has been extended. Intermediate adducts involv- ing the 5,6-double bond have been shown to be components of the reaction mixture from the acetoxydiene and bromine in acetic acid.
Acid catalysed iso~nerisation and rearrangements of the kinetically controlled products, and dibrornination, can be controlled by
selective choice of the conditions of bromination and work-up.
Complications associated with the reaction paths have been partly elucidated. The rates and mechanis~n of reversible isomerisation of 6B- to 6a-bromocholest-4-en-3-one, and of 2a,B
-
to 2a,6a-dibromocholest-4-en-3-one, have been studied and a proposed mechan- ism is outlined.
