Catalytic Oxidative Cyclizations Mediated by Osmium

Significance

An osmium-catalyzed oxidative cyclization of hydroxy amines has been developed which generates pyrrolidines or THF’s in high yield with high diastereoselectivity. Preferentially five-membered rings are formed (THFs if alcohol is appropriately located, pyrrolidine if amine is appropriately located), but the nitrogen heterocycle dominated in a competition experiment (see above). OsO₄ was found to be the best catalyst for pyrrolidine synthesis, while K₂OsO₂(OH)₄ was the catalyst of choice for THF synthesis. A variety of substituted hydroxy amines are tolerated including those with bulky t-Bu groups appended directly to the alkene. A nice competition experiment was performed which showed only formation of the pyrrolidine with no sign of THF formation.