A Three-Step Synthesis of the Guaianolide Ring System



By using a gallium(III) triflate catalyzed intramolecular (4+3) cycloaddition, a few functionalized furan-derived tricycles that share the common guaianolide sesquiterpene ring system were prepared in a stereoselective manner in only three steps from commercially available starting materials. A discussion of the formation of alternative products is included, with possible substrate requirements to achieve the key cycloaddition step in an efficient way.