CHEMOSELECTIVE REDUCTION OF ALPHA,BETA-EPOXY CARBONYL-COMPOUNDS TO BETA-HYDROXY CARBONYL-COMPOUNDS (ALDOLS AND THEIR ANALOGS) BY ORGANOSELENIUMS AND ITS APPLICATION TO NATURAL PRODUCT SYNTHESIS

Novel methods for the reduction of alpha, beta-epoxy ketones, alpha, b eta-epoxy esters (glycidic esters), and their congeners to beta-hydrox y carbonyl compounds (aldols) by the use of organoselenium reagents ar e described. The reagents, a sodium phenylseleno(triethyl)borate compl ex Na[PhSeB(OEt)(3)] easily prepared by reduction of (PhSe)(2) with Na BH4 in EtOH and benzeneselenol (PhSeH) generated in situ from the bera te complex by addition of acetic acid, have been demonstrated to serve as excellent reducing agents for these transformations. The organosel enium-mediated reduction of alpha, beta-epoxy carbonyl compounds regio specifically occurs at the alpha-carbon to produce a wide variety of c yclic (intramolecular) aldols as well as acyclic (intermolecular) ones in excellent yields. Quantitative mechanistic studies have revealed t hat the organoselenium-mediated reduction proceeds via an alpha-substi tution process in contrast to the common electron transfer reducing ag ents. Application of the methods to natural product synthesis such as santanolides (dehydroisoerivanin, isoerivanin, ludovicin C, and 1 alph a, 3 alpha-dihydroxyarbusculin B), diarylheptanolides (yashabushiketol , yashabushiketodiol A and yashabushiketodiol B), plant toxins picroto xinin and picrotin, and a corn host-specific pathotoxin PM-toxin A is described.