Desymmetrization of Prochiral Cyclobutanones via Nitrogen Insertion: A Concise Route to Chiral γ-Lactams

Asymmetric access to gamma-lactams is achieved via a cyclobutanone ring expansion using widely available (1S,2R)-1-amino-2-indanol for chiral induction. Mechanistic analysis of the key N,O-ketal rearrangement reveals a Curtin-Hammett scenario, which enables a downstream stereoinduction (up to 88:12 dr) and is corroborated by spectroscopic, crystallographic, and computational studies. In combination with an easy deprotection protocol, this operationally simple sequence allows the synthesis of a range of optically pure gamma-lactams, including those bearing all-carbon quaternary stereocenters. In addition, the formal synthesis of drug molecules baclofen, brivaracetam, and pregabalin further demonstrates the synthetic utility and highlights the general applicability of the presented method.

Automated summary

Asymmetric access to gamma-lactams was achieved using (1S,2R)-1-amino-2-indanol for chiral induction, with downstream stereoinduction up to 88:12 dr. Mechanistic analysis revealed a Curtin-Hammett scenario, supported by spectroscopic, crystallographic, and computational studies. The method allows for the synthesis of optically pure gamma-lactams, including those with all-carbon quaternary stereocenters, and is exemplified by the formal synthesis of drug molecules baclofen, brivaracetam, and pregabalin.