Tandem 5-Exo-dig-5-exo-trig Radical Cyclization leading to a 6,5-Ring Fused Carbobicycle possessing Two Contiguous Quaternary Carbons at the Bridgehead and its Adjacent Positions

Abstract

The tin-mediated tandem 5- exo-dig-5- exo-trig radical cyclization of dibromoacetal 4a stereoselectively gives the angular 6,5,5-ring fused tricycle 6 via spirocyclic acetal 5 in 93% yield.