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 1a-h 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 2a-h after acidic workup. When enamide 1d was treated with Bu3SnH 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.

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