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 diastereoselective cyclization upon reaction with epoxides in presence of [Cp2TiCl]2. trans-Fused tetrahydropyranosylidene complexes are obtained from the radical addition of cyclohexene oxide to monosaccharide-derived vinylcarbene tungsten complexes. The benzyl-protected 1,2-anhydro-α-d-glucopyranose adds to styryl and alkynyl carbene complexes to give bicyclic trans-fused tetrahydro- and dihydropyranosylidene complexes as well as the acyclic addition products.