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. Capital catalysts: The osmium‐catalyzed cyclization of o‐alkynyl phenethylamines enabled the straightforward preparation of a broad range of dopaminergic 3‐benzazepine derivatives. More commonly used metal catalysts did not promote the desired reaction efficiently. Mechanistic investigations revealed that the process takes place via osmacyclopropene intermediates, examples of which were isolated and characterized by X‐ray diffraction analysis.