Herein, we report the convergent total syntheses of (-)-mollfoliagein A and (-)-rhodomollein XXV, two highly oxygenated grayanoids featuring a synthetically challenging oxa-tricyclo3.3.1.03.7nonane structure unit. The characteristic 5/7/6/5/5 skeleton of mollfoliagein A was constructed in a single step from two fragments via a Stille carbonylative coupling/transannular oxa-Michael addition/vinylogous Knoevenagel condensation cascade. Other salient features are the C/D ring formation by reshaping the bicyclo3.3.0octene unit to the highly functional bicyclo3.2.1octane ring system and PPTS mediated procedure for converting (-)-mollfoliagein A to (-)-rhodomollein XXV.
Du et al. (Mon,) studied this question.