The direction of ring opening of trans-α-methylstilbene oxide by organic acids

Abstract

In the reaction of mesitoic acid with trans-α-methylstilbene oxide the anion adds exclusively to the tertiary carbon atom, to give the hydroxy ester of type III, which also can be prepared from α-methylbenzoin mesitoate with KBH 4 and is transformed into the isomeric ester of type V by the action of alkali; the latter ester also being formed by reaction of threo-1,2-diphenyl-1,2-propanediol with mesitoyl chloride. Other acids yields only esters of type V, probably formed from primary products of type III by a rapid acyl group shift. All esters thus prepared belong to the threo series; corresponding erythro esters were prepared for comparison. The reductions of α-methylbenzoin acetate and mesitoate with LiA1H 4 produce exclusively threo-1,2-diphenyl-1,2-propanediol, in contrast with the low stereoselectivity of the similar reduction of α-methylbenzoin itself.