Carbohydrate-modified fused pyranosylidene complexes via radical addition of epoxides to unsaturated metal carbenes

Alkenyl and alkynyl carbene complexes of chromium and tungsten undergo a di astereoselective cyclization upon reaction with epoxides in presence of [Cp 2TiCl](2). trans-Fused tetrahydropyranosylidene complexes are obtained from the radical addition of cyclohexene oxide to monosaccharide-derived vinylc arbene tungsten complexes. The benzyl-protected 1,2-anhydro-alpha-D-glucopy ranose adds to styryl and alkynyl carbene complexes to give bicyclic trans- fused tetrahydro- and dihydropyranosylidene complexes as well as the acycli c addition products. (C) 2000 Elsevier Science Ltd. All rights reserved.