Sesquiterpene synthesis via tandem radical cyclization of N-Aziridinylimines

Abstract

Radical cyclization of N-aziridinylimines provides a ready access to 5- and 6-membered ring radicals, in which N-aziridinylimines are used as geminal radical acceptor and donor equivalents. The formation of consecutive carbon-carbon bond is achieved by tandem radical cyclizations. This approach is unique and has great synthetic potential, particularly for the construction of quaternary carbon centers. Based on characteristics involving radical reactions of N-aziridinylimines, zizaene family sesquiterpenes such as dl-zizaene and dl-khusimone are synthesized utilizing the tandem radical cyclization reactions of N-aziridinylimines forming tricyclo$[6.2.1.0^{1,5}]$-undecane skeletons. Angular fused triquinane dl-pentalenene bearing tricyclo$[6.3.0.0^{4,8}]$undec-2-ene ring system, three cyclopentane rings and one quaternary carbon center at the ring junction, is also synthesized by the consecutive carbon-carbon bond formation approach. The synthesis of dl-nudenoic acid having tricyclo$[5.4.1.0^{4,5}]$dodecane skeleton which is lately discovered from liverwort species is attempted. Many efforts to synthesize the tricyclic skeleton, especially the main skeleton of dl-nudenoic acid, from this approach was not successful.