Highly Diastereoselective Synthesis of γ-Lactams Enabled by Photoinduced Deaminative [3 + 2] Annulation Reaction.

The photoinitiated deaminative [3 + 2] annulation reaction of N -aminopyridinium salts with alkenes for the synthesis of functionalized γ-lactams is described. This transformation shows good functional group tolerance as well as excellent diastereoselectivity. Preliminary studies suggest that the employed N -aminopyridinium salts generate the key amidyl radical intermediates through N-N bond cleavage via a photoinduced single-electron transfer (SET) process. The amidyl radical species would add to the double bond of alkenes, followed by a radical-mediated annulation process, to afford the desired γ-lactams.