L-Selectride reductions a-Silylated ketones 5 or 10 of high enantiomeric purity (ee 2 goo/,) are easily available by silylation or silylation/alkylation of ketones 1 or 6, resp., according to the SAMP/RAMP hydrazone method. Reduction of 5 or 10 with L-selectrideg, followed by oxidative cleavage of the C-Si bond, leads to vic-diols 11 -13 with high diastereoselectivity (de 2 90%) and without racemization. The stereoselectivity of the reduction depends on the structure of the a-silyl ketones 5 or 10, the reducing reagents, and the solvents used.Asymmetric synthesis of uic-diols has recently received considerable attention, because vic-diols are common structural features of many natural products'), useful chiral building blocks in the synthesis of biologically active compounds'), and valuable intermediates in a variety of synthetic transformations ' 1.These approaches have been carried out by enantioselective ring opening by epoxide hydrase4', ring opening by diastereoselective epoxidation of chiral allylic alcohols "chiral pool" syntheses from natural products6) including diastereoselective 1,2-additions of organometallics to a-alkoxy aldehydes &), stereospecific coupling of chiral boronic esters with chiral lithio esters followed by hydrolysis7), homologation of alkylboronates followed by hydrolysis *), and asymmetric osmylation of olefins with chiral amines as ligands'). On the other hand, stereoselective reductions to form uicdiols have also been described based on diastereoselective reduction of a-hydroxy ketones'"), but little attention has been paid to enantioselective syntheses of vic-diols by enantio-and diastereoselective reductions, although in the realm of aliphatic ketones efficient techniques") are now at hand to selectively introduce stereocenters on acyclic carbon chains '*). Therefore, the development of still more versatile and effective diastereo-and enantioselective syntheses of uic-diols is of considerable interest.In continuation of our efforts to further explore the utility of the SAMPIRAMP hydrazone method13), we now report on a convenient synthesis of vic-diols with high regio-, diastereo-and enantioselectivity. Enantioselective Synthesis of a-Silyl Ketones 5 and 10 a-Silyl Ketones 5 and 10 were synthesized from symmetrical dialkyl ketones 1 or unsymmetrical methyl alkyl ketones 6 according to Schemes 3 and 4.Symmetrical dialkyl ketones 1, after conversion into their corresponding SAMP hydrazones (S)-2, are metalated with lithium diisopropylamide and then a-C-silylated with isopropoxydimethylsilyl chloride.The a-silylated SAMP hydrazones 3 (de 2 90%) thus obtained are cleaved oxidatively and free of racemization with ozone affording, after chromatographic separation of (S)-4 (recycling of the chiral auxiliary), the ct-silyl ketones (R)-5 of high enantiomeric purity
