Photocyclisations of dicyclopent-1-enyl methanes to tricyclo[6.3.0.02,6]undecanes: a synthesis of the hirsutane carbon skeleton

Abstract

Irradiation of the dicyclopent-1-enyl-methane (4) in methanol leads to [2 + 2] cycloaddition, followed by in situ addition of methanol to the presumed intermediate bicyclo[2.1.0]pentane (5) producing the cis,syn,-cis-tricyclo[6.3.0.0^2,6]undecane (6) in high yield; the general method is applied in a synthesis of the hirsutane carbon skeleton found in hirsutic acid (1) and related natural sesquiterpenes.