Synthesis of γ‑, δ‑, and ε‑Lactams by Asymmetric Transfer Hydrogenation of <i>N</i>‑(<i>tert</i>-Butylsulfinyl)iminoesters

Abstract

Highly enantiomerically enriched γ- and δ-lactams have been prepared by a simple and very efficient procedure that involves the asymmetric transfer hydrogenation of <i>N</i>-(<i>tert</i>-butylsulfinyl)­iminoesters followed by desulfinylation of the nitrogen atom and spontaneous cyclization to the desired lactams during the basic workup procedure. Five- and six-membered ring lactams bearing aromatic, heteroaromatic, and aliphatic substituents have been obtained in very high yields and ee’s up to >99%. A slight modification of the procedure also allowed the preparation of ε-lactams in good yields and very high enantioselectivities. Both enantiomers of the final lactams could be prepared with equal efficiency by changing the absolute configuration of the sulfinyl chiral auxiliary