Allylic Rearrangements. XXI. Further Studies Related to the Nature of the Butenyl Grignard Reagent

Cleavage of the butenyl Grignard reagent by water gives a mixture of butenes, although the products from a variety of addition and coupling reactions are almost exclusively α-methylallyl derivatives. To gain further information regarding the butenyl Grignard reagent we have turned to the study of some reactions expected to cleave the reagent to butenes through the operation of mechanisms different from that involved with water. For the cleavage of butenylmagnesium bromide by an enolizable ketone, acetomesitylene was chosen since several investigators have shown that organometallic compounds such as ethylmagnesium bromide, n-butyllithium and phenylsodium do not add to the carbonyl group of this compound but give enolization products exclusively. Contrary to expectation, the reaction of butenylmagnesium bromide with acetomesitylene gave a negligible amount of enolization products (less than 3% of the calculated amount of butenes was detected). From the reaction mixture was recovered about 12% of the original ketone and the principal product was the tertiary alcohol, α-methylallylmesitylmethylcarbinol (I). The yield was 83%