Osmium-mediated oxidative cyclizations: A study into the range of initiators that facilitate cyclization

A general route to prepare substituted, saturated five-membered heterocycles has been developed. The application of a wide range of starting materials to the osmium-catalyzed oxidative cyclization reaction is described. Diols, hydroxy-amides, hydroxy-sulfonamides, and carbamates all cyclize in moderate to excellent yields to give cis-tetrahydrofurans and pyrrolidines, depending upon the position of the heteroatoms in the starting materials. These cyclizations all proceed with near total selectivity for the cis-hetero-cycles, and with stereospecific introduction of a hydroxy group adjacent to the ring. Moreover, routes to enantiopure starting materials are described, which give enantiopure products upon cycli-zation. Catalyst loadings of as low as one mol percent have been successfully employed for this transformation.