Enantioselective synthesis of a tetrasubstituted oxocane via a double diastereoselective hetero Diels-Alder reaction

A procedure for the enantioselective preparation of tetra-substituted mediu m sized cyclic ethers is presented. An oxocane is prepared by a sequence wh ich involves a double diastereoselective hetero Diels-Alder reaction betwee n a chiral aldehyde and a diene bearing an allylic chiral centre. The cyclo adduct is transformed into a linear ether which is then converted to the cy clic ether by a highly regioselective intramolecular alkylation of a lithio sulfone with an epoxide. The sense of induction of the chiral centre on the diene is discussed.