Stereoselective addition of organomanganese reagents to chiral acylsilanesand aldehydes

Organomanganese halides and organomanganates prepared by transmetalation of organolithium and Grignard reagents add smoothly to the carbonyl moiety of acylsilanes and of substituted aldehydes bearing a chiral center at the al pha -position affording the desired alcohols in good to excellent yields an d with essentially no undesired products from enolization. Comparison of th e stereochemical outcome with that observed for other organometallic specie s, outlines the capability of organomanganese reagents to induce uniformly good diastereoselectivities, in a number of cases significantly higher than reported previously for these reactions. The key role displayed by the R,S I group in promoting high 1,2-asymmetric induction, clearly emerges in the comparison of acylsilane 12 with the corresponding aldehyde 13. The sense o f the Cram/anti-Cram selectivity depends upon the nature of the carbonyl re agents engaged in these reactions. (C) 2001 Elsevier Science B.V. All right s reserved.