Abstract
Investigations of (+) alphagamma-dimethylallyl alcohol led to the belief that an optically active product would be obtained when (-)alpha-phenyl-gamma-methylallyl alcohol (and its derivatives) was converted into alpha-phenyl-gamma-methylallyl alcohol (and its derivatives). This expectation has been fully realized; the hydrogen phthalic ester of alpha-phenyl-gamma-methylallyl alcohol changes into the isomeric ester containing 87% of one optical enantiomorph. The transformation CHPhX. CH: CHMe → CHPh:CH.CHXMe also proves to be an exceptionally convenient anionotropic system for investigation since the more reactive esters of alpha-phenyl-gamma-methylallyl alcohol change into their isomerides at ordinary temperatures either in solution or (in the case of the hydrogen phtalio ester) in the crystalline state. By using optically active compounds this change can readily be followed polarimetrically, and thus a convenient and accurate method of studying the reaction is available. Like the hydrogen phthalio ester of alphagamma-dimethylallyl alcohol, esters of alpha-phenyl-gamma-methylallyl alcohol undergo conversion in methylalcoholic and acetic solution and yield respectively the methyl ether and the acetic ester of alpha-phenyl-gamma-methylallyl alcohol. Esters of alpha-phenyl-gamma-methylallyl alcohol undergo similar replacement reactions but much more slowly. On addition of bromine, (+)gamma-phenyl-alpha-methylallyl alcohol yields two methyl-alphabeta-dibromo-beta-phenylethyl oarbinols which may be separated by fractional crystallization. One of these, on oxidation, yields (+)methyl-alphabeta-dibromo--phenyl ethyl ketone, while the other gives the (-)-enantiomorph possessing numerically the same rotatory power. When bromine is Added to (+) gamma-phenyl-alpha-methylallyl and the mixture oxidised without any form of previous separation the resulting ketone is optically active. As the original centre of asymmetry in the compound has been destroyed by oxidation this reaction represents a new type of asymmetric synthesis.