Regio- and Stereospecific Cyclizations of Germacrones

Abstract

From a biogenetic point of view, the acid-catalyzed cyclizations of germacrones (1, 2, and 3) were carried out, using several kinds of reagents and solvents (80% aq AcOH, 80% aq HCOOH, AlCl₃ in absolute ether, AcOH in PhSH, 100% HCOOH in PhSH, and concd H₂SO₄ in PhSH). In all cases, the stereospecific cyclizations of these germacrones took place to give cadinane-type, selinane-type or guaiane-type compounds depending on the kinds of reagents and solvents. The formation process of each compound will be presented in detail.