New Pathways in Transannular Cyclization of Germacrone [Germacra-1(10),4,7(11)-trien-8-one]: Evidence Regarding a Concerted Mechanism

Abstract

The transannular cyclization of germacrone with HSO(3)Cl at -78 degrees C by means of a concerted and regioselective mechanism gives rise to a bicyclo[6.2.0]decan-2-ylium intermediate ion, which evolves to unusual skeletons through subsequent cyclization and Wagner-Meerwein rearrangements. This novel germacra-1(10),4-diene cyclization could suggest the existence of a new biosynthetic pathway to sesquiterpenes.