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 LiCIO₄ 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.