| Catalytic reactions involving transition metal-coordinated vinylidene complexes as reactive intermediates have been investigated. Based on the facile formation of ruthenium-oxacarbene complexes from homopropargylic alcohols, a ruthenium-catalyzed oxidative cyclization of homopropargylic alcohols was developed employing N-hydroxysuccinimide as a mild oxidant. Extrapolation of this method to bis-homopropargylic alcohols led to a divergent ruthenium-catalyzed reaction of bis-homopropargylic alcohols that provides a convenient access to either dihydropyrans or valerolactones. This method was applied to a highly flexible approach towards trans-fused polycyclic tetrahydropyrans. The ability to form Rh vinylidene complexes from terminal alkynes was utilized in the development of Rh-catalyzed cycloisomerization of homopropargylic and bis-homopropargylic alcohols. Among the transition metals that perform similar reactions, rhodium catalysts demonstrate the best chemoselectivity and turnover numbers to date. |
