CHEMOENZYMATIC DERACEMIZATION OF (+ -)-2,2-DISUBSTITUTED OXIRANES/

The preparation of vicinal diets in up to 98% e.e. and 98% yield from the corresponding (+/-)-2,2-disubstituted epoxides was achieved via an enantioconvergent two-step hydrolysis: Thus, enantioselective enzymat ic hydrolysis of the (S)-epoxide proceeded with retention of configura tion furnishing the corresponding (S)-diol. In a subsequent step, the remaining (R)-oxirane was hydrolyzed during workup under acid catalysi s with complete inversion of configuration yielding the (S)-diol. A de tailed study of the latter reaction revealed that the experimental con ditions have to be carefully chosen with respect to (i) nature of the acid, (ii) the solvent, and (iii) its water content to avoid racemizat ion. (C) 1997 Elsevier Science Ltd. All rights reserved.