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 ANALOGS

Novel methods for the reduction of alpha,beta-epoxy ketones, alpha,bet a-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 NaBH 4 in EtOH and benzeneselenol (PhSeH) generated in situ from the borate complex by addition of acetic acid, have been demonstrated to serve a s excellent reducing agents for these transformations. The organoselen ium-mediated reduction of alpha,beta-epoxy carbonyl compounds regiospe cifically occurs at the alpha-carbon to produce a wide variety of cycl ic (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-substitut ion process in contrast to the common electron transfer reducing agent s. (C) 1997 Elsevier Science Ltd.