The organoselenium-mediated reduction of alpha,beta-epoxy ketones, alpha,beta-epoxy esters, and their congeners to beta-hydroxy carbonyl compounds: Novel methodologies for the synthesis of aldols and their analogues

Novel methods for the reduction of alpha,beta-epoxy ketones, alpha,beta-epoxy esters (glycidic esters), and their congeners to beta-hydroxy carbonyl compounds (aldols) by the use of organoselenium reagents are described. The reagents, a sodium phenylseleno(triethyl)borate complex Na[PhSeB(OEt)(3)] easily prepared by reduction of (PhSe)(2) with NaBH4 in EtOH and benzeneselenol (PhSeH) generated in situ from the borate complex by addition of acetic acid, have been demonstrated to serve as excellent reducing agents for these transformations. The organoselenium-mediated reduction of alpha,beta-epoxy carbonyl compounds regiospecifically occurs at the alpha-carbon to produce a wide variety of cyclic (intramolecular) aldols as well as acyclic (intermolecular) ones in excellent yields. Quantitative mechanistic studies have revealed that the organoselenium-mediated reduction proceeds via an alpha-substitution process in contrast to the common electron transfer reducing agents. (C) 1997 Elsevier Science Ltd.