Studies on the synthesis of tricyclic ring through the rearrangement of free radicals

Abstract

Radical cyclization reactions of silyl enol ethers (11, 12, 22, 31), acyclic (33, 45) and cyclic enynes (53, 61) were studied to examine the scope and the limitation of tricyclic ring formation as well as the selectivity of the cyclization reaction. Unlike the cyclization of cyclopentene ring system 31, cyclization reactions of acyclic olefin and cyclic compounds with exo cyclic olefins produced mixtures of diastereomeric bicyclic or tricyclic compounds. The regioselective cyclization of 31 was obtained through the conformational preference of hydroxylated butynyl chain. In the cyclization reaction of cyclic endo olefin 66, rearranged bicyclic product was produced. Tricyclo dodecane ring system was produced through tandem radical cyclization. This rearrangement was extended to 7-membered endo cyclization. The radical cyclization reaction of 75 produced 7-endo product 76b as well as normal cyclization product 76a.