An Allenic Pauson-Khand Approach to 6,12-Guaianolides

Cyclocarbonylation of alpha-methylene butyrolactone-containing allene-ynes affords 6,12-guaianolide ring systems. Incorporation of the a-methylene butyrolactone early in a synthetic sequence is rare for reactivity reasons; however, this moiety proves to be beneficial to the allenic Pauson-Khand reaction. The three double bonds and the ketone in the resulting 5-7-5 ring system bear significant differences in their reactivity and are ideally positioned for synthetic application to 6,12-guaianolides and analogs.