Facile and selective formation of a linear-triquinane skeleton by a rationally designed round trip radical reaction

The radical reaction of 1-iodo-1,5,10-trienoate afforded a linear fused five-membered carbocycle. Another key feature of this reaction is the remarkable acceleration of the reaction rate and enhancement of selectivity caused by the introduction of a conjugated ester moiety at the terminal olefin. This cascade reaction proceeds through three sequential 5-exo cyclizations. The result is in stark contrast with the previously reported radical reaction of 1-iodo-1,5,9,14-tetraenoate, which afforded a linear fused six-membered carbocycle through a 6-endo, 6-endo, 6-exo cyclization.