Catalytic Cyclization of o-Alkynyl Phenethylamines via Osmacyclopropene Intermediates: Direct Access to Dopaminergic 3-Benzazepines

A novel osmium-catalyzed cyclization of o-alkynyl phenethylamines to give 3-benzazepines is reported. The procedure allows the straightforward preparation of a broad range of dopaminergic 3-benzazepine derivatives. Mechanistic investigations revealed that the process takes place via osmacyclopropene intermediates, which were isolated and characterized by X-ray crystallography.