STEREOSELECTIVE SYNTHESIS OF HIGHER SUGARS BY HOMOLOGATION OF CARBOHYDRATE-DERIVED ENALS WITH NONRACEMIC GAMMA-(SILYLOXY) ALLYLIC STANNANESAND SUBSTRATE-DIRECTED HYDROXYLATION

A strategy is described for the chain extension of carbohydrate deriva tives utilizing sequential Horner-Emmons condensation and then reducti on-oxidation to prepare the enal homologue VII, which is converted to the corresponding dienyl bis-OTBS derivative IX upon condensation with a gamma-(silyloxy) allylic stannane VI and subsequent silylation. Dih ydroxylation of dienes M with OsO4-NMO leads to syn,anti,syn,anti,syn. hexol derivatives X with excellent diastereoselectivity. These hexols undergo selective oxidative cleavage with H5IO6 to yield gamma-lactol s XI. The methodology has been used to prepare the octonic lactone 15 from (S,S)-dimethyl tartrate and the undeconic lactone 32 from D-manni tol.