Efficient synthesis of enantiopure conduritols by ring-closing metathesis

Two short synthetic approaches to enantiopure conduritols are described starting from the chiral pool. In both cases, the cyclohexene ring is assembled via ring-closing olefin metathesis. The terminal diene precursers for the metathesis reaction are prepared either from octitols or from tartaric acids. The farmer route involves a new method for selective bromination of the primary positions in long-chain carbohydrate polyols. Subsequent reductive elimination with zinc then generates the diene. The latter route uses a highly diastereoselective addition of divinylzinc to tartaric dialdehydes for preparation of the dienes.