Bismuth-Catalyzed Synthesis of 2,6-Disubstituted Dihydropyrans

Over the last few years, bismuth has become a frequently used Lewis acid both for silyl protection and deprotection (see book below) but also in the synthesis of dihydropyrans (P. A. Evans, J. Cui, S. J. Gharpure, R. J. Hinkle J. Am. Chem. Soc. 2003, 125, 11456-11457). In the present paper, the authors develop a new bismuth-catalyzed route towards 2,6-disubstituted dihydropyrans via a silyl-Prins reaction that compares favorably to the method described by Dobbs and MartinovicŽ using indium (Tetrahedron Lett. 2002, 43, 7055-7057).