The extent of the asymmetric addition of dialkylzincs to chiral a-siloxyaldehydes is determined by the configuration of the chiral catalyst and not by the chirality of a-siloxyaldehydes, providing either diastereoisomer of monoprotected vicinal diols in high diastereoisomeric excess.The direction of diastereoselectivity in the addition of alkylmetal reagents to a-chiral a-alkoxy-and a-siloxy-aldehydes is an important problem .1 Diastereodivergent alkylation of these carbonyl compounds requires the use of alkylmetal reagents of different structures for different diastereoselectivichiral catalyst (lS, 2R)-5 1 I ChKalCatalyst (1 R, 23-30 R ' . . P #O OH a; R' = Me, R2 = But(Ph2)Si (4 m-5 a; R' = Me, R2 = But(Ph2)Si, R3 = Et b; ~1 = w, ~2 = ph3si, ~3 = ~t b; R' = Me, R2 = Ph3Si d; R' = ph, R2 = (P&Si C; R' = Ph, R2 = Bu'(Ph2)Si c; R' = Ph, R2 = But(Ph2)Si, R3 = Et d; R' = Me, R2 = But(Ph2)Si, R3 = Me 6; R' = Ph, R2 = (Pi)3Si, R3 = Et chiral catalysts Ph. .Me (1 S,2R)-(-)-% (DBNE) (1 R,ZS)-(+)-3a Me (S)-( +)-3 b (DPMPM)
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