Iridium‐Catalyzed Reductive (3+2) Annulation of Lactams Enabling the Rapid Total Synthesis of (±)‐Eburnamonine

Abstract

A reductive (3+2) annulation of lactams through iridium‐catalyzed hydrosilylation and photoredox coupling with α‐bromoacetic acid was developed. The iridium‐catalyzed hydrosilylation of the lactam carbonyl group and subsequent elimination provide a transient cyclic enamine, which undergoes iridium‐catalyzed photoredox coupling with α‐bromoacetic acid in a one‐pot process. The developed conditions show high functional‐group tolerance and provide cyclic N,O‐acetals containing a quaternary carbon center. The resulting N,O‐acetals undergo a variety of acid‐mediated nucleophilic addition reactions via iminium ions to give substituted cyclic amines. The developed sequence including reductive (3+2) annulation and acid‐mediated nucleophilic addition was successfully applied to the four‐step total synthesis of (±)‐eburnamonine.