Bu3SnH-mediated 5-exo selective radical cyclization of N-vinyl-α,β-unsaturated amides leading to γ-lactams

Treatment of N-vinyl-α,β-unsaturated amides with Bu3SnH and a catalytic amount of AIBN in boiling benzene caused 5-exo cyclization of allylic O-stannyl ketyl radicals generated by addition of Bu3Sn· on the amide-oxygen atoms to provide γ-lactams after acidic workup. When enamide was treated with Bu3SnH in the presence of AIBN followed by aldehydes , sequential radical cyclization and aldol reactions occurred to afford anti-adducts and syn-adducts .