Bu3snh-mediated 5-exo selective radical cyclization of N-vinyl-α,β-unsaturated amides leading to γ-lactams

Abstract Treatment of N -vinyl-α,β-unsaturated amides 1a – h with Bu 3 SnH and a catalytic amount of AIBN in boiling benzene caused 5-exo cyclization of allylic O -stannyl ketyl radicals generated by addition of Bu 3 Sn· on the amide-oxygen atoms to provide γ-lactams 2a – h after acidic workup. When enamide 1d was treated with Bu 3 SnH in the presence of AIBN followed by aldehydes 3a – d , sequential radical cyclization and aldol reactions occurred to afford anti -adducts 4a – d and syn -adducts 5a , b .