Stereoselective synthesis of long-chain polyols by sequential homologation of enals with nonracemic .gamma.-silyloxy allylic stannanes and directed hydroxylation

The nonracemic γ-silyloxy allylic stannanes (S)-8 and (R)-8 add to the (R,R)-tartrate derived enals 7 and 24 to afford the adducts alkadienol 9, 14, and alkatetraenediol 25. The bis-TBS derivatives 10, 15 and 22, upon hydroxylation with catalytic OsO 4 -NMO, yield the differentially protected polyols 11, 16, and 24