Rhodium-catalyzed intramolecular cyclization for synthesizing thiodihydropyrans.

Addressing the challenge of constructing multi-substituted dihydropyrans, we present an efficient synthesis method for oxygen-containing heterocycles. Using thiones and metal carbenes, we employed xanthate and triazole to intramolecularly synthesize dihydropyran or dihydrofuran compounds. 1,2-Hydride migration was inhibited, and thiodihydropyrans were obtained in excellent yields. A mechanism proceeding through a Rh-carbene intermediate is proposed for the multi-substituted dihydropyrans synthesis.