Alpha beta-Epoxy ketones on treatment with baker's yeast yield different types of products depending on their substitution. Small groups such as H or Me attached at the epoxy end protect that end from attack. Thus, 1-acyl epoxides with H, methyl or propyl as the 2-epoxy substituent give solely the epoxy alcohol product with moderate stereoselectivity (13-64% d.e.). With a 2-phenyl substituent the sole product is the 1.2.3-triol as a single racemic diastereoisomer derived by a reduction/hydrolysis sequence involving a syn ring-opening of the epoxide. More than one enzyme is probably involved in both of these transformations which tend to favour S-reduction. The detailed mechanism of product formation in both processes has been undertaken and the formation of the triols has been shown by O-18 labelling studies to involve asymmetric reduction of the ketone and a double inversion during epoxide ring-opening involving a carbocation intermediate.
Reference:
Meth-Cohn, O, Horak, RM and Fouche, G. 1994. Bakers yeast-mediated transformations of alpha-keto epoxides. Journal of the Chemical Society-Perkin Transactions 1, pp 1517-1527
Meth-Cohn, O., Horak, R., & Fouché, G. (1994). Bakers yeast-mediated transformations of alpha-keto epoxides. http://hdl.handle.net/10204/815
Meth-Cohn, O, RM Horak, and Gerda Fouché "Bakers yeast-mediated transformations of alpha-keto epoxides." (1994) http://hdl.handle.net/10204/815
Meth-Cohn O, Horak R, Fouché G. Bakers yeast-mediated transformations of alpha-keto epoxides. 1994; http://hdl.handle.net/10204/815.