Studies on the rearrangement of free radicals and its application to the synthesis of tricyclo[4.3.2.0 1,5]undecane ring system

Abstract

The radical cyclization and the rearrangement of model compound 2 were studied. Enyne 2 under radical cyclization condition gave a mixture of 5-exo product and the rearranged 6-endo product. As the concentration of $Bu_3SnH$ was diluted, the ratio of 6-endo product to 5-exo product increased. Substituents at $C_1$ and $C_2$ is important for the radical rearrangement. When various hydride sources ($Ph_3GeH, (TMS)_3SiH$ and $PhSH$) are used, the similar kinetic results were obtained. Also, stabilization the radical intermediate by these groups is important for the rearrangement. Tricyclo[4.3.2.0 1,5]undecane ring system was synthesized through tandem radical reaction sequence which involved the rearrangement. Several dienynes and endiynes under radical cyclization uniformly produced the tricyclic compounds. This tandem radical reaction would be applied to the synthesis of the natural products.