Desymmetrization of prochiral cyclobutanones via nitrogen insertion : a concise route to chiral γ-lactams
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Abstract
Asymmetric access to γ-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 γ-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.
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Angewandte Chemie : International edition, 60, 17, Wiley-VCH, Weinheim, 2021, https://doi.org/10.1002/anie.202100642