Total Syntheses of Cannabicyclol, Clusiacyclol A and B, Iso-Eriobrucinol A and B, and Eriobrucinol

Total syntheses of a series of chromane natural products that contain a cyclobutane ring are described. A unified theme in the strategy employed for all these syntheses is an oxa-[3 + 3] annulation for constructing the chromane nucleus and a stepwise cationic [2 + 2] cycloaddition for the cyclobutane formation. More importantly, the two reactions could be rendered in tandem, thereby providing an expeditious approach to this family of natural products.