Reaction of dianions of acetoacetic esters with epibromohydrin derivatives: A novel synthesis of tetrahydrofuran derivatives 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.