alpha.-Amino acids as chiral educts for asymmetric products. Chirospecific syntheses of methyl L-sibirosaminide and its C-3 epimer from L-allothreonine

Efficient syntheses of methyl L-sibirosaminide and its C-3 epimer are described using L-allothreonine as the chiral educt. Amino acylations of organometallics with the lithium salt of N-(phenylsulfonyl)-L-allothreonine constitute the key carbon-carbon bond-forming steps. The resulting methyl and vinyl ketones are then converted to tertiary alcohols by a second organometallic addition, and the order of addition controls the stereochemistry at the new chiral center. Stereocontrolled functionalization of the vinyl group then leads to the amino sugars. Elaboration to the C-3 epimer of sibirosamine was achieved via a Pummerer oxidation route, while in the preparation of sibirosamine itself a selective tetraol oxidation route was used.