Radical Cascade Reaction in Heterocyclic Synthesis: Formation of Bicyclic 2,3‐dihydrostannoles and Other Heterocyclic Compounds from Amide‐type 1,6‐Enyne Compounds

Abstract

AbstractAmide‐type 1,6‐enyne compounds, readily available from unsaturated N‐Boc acyl amide and propargylic mesylate, underwent a radical cascade reaction upon treatment with Bu3SnH, giving bicyclic 2,3‐dihydrostannole lactams in good yields. Regioselectivity of the reaction depended on the presence or absence of alkyne substituents; alkyl‐substituted internal alkynes selectively gave 2,3‐dihydrostannoles in good yields, while terminal alkynes gave a mixture of piperidine and 2,3‐dihydrostannole. The reaction promoted the radical cascade process starting from the addition of tin radical to the alkenyl terminal followed by 5‐exo‐dig radical cyclization. The resulting vinyl radical attack the tin atom, and direct radical substitution progressed, giving bicyclic 2,3‐dihydrostannoles in good yields.