Preparation of novel synthons, uniquely functionalized tetrahydrofuran and tetrahydropyran derivatives

The dianion of the acetoacetic ester reacts with epibromohydrin derivatives to afford a mixture of (Z)-2-alkoxycarbonylmethylidenetetrahydrofuran derivative and (E)-2-alkoxycarbonylmethylidenetetrahydropyran derivative. The selective formation of the tetrahydrofuran derivative is achieved by the use of LiClO4 as the additive. The preparation of the optically active tetrahydrofuran derivatives and tetrahydropyran derivatives is also examined, and the optical purity and absolute configuration of the products is elucidated.