Enantioselective Total Syntheses of Grayanoid (−)-Mollfoliagein A and (−)-Rhodomollein XXV

Herein, we report the convergent total syntheses of (-)-mollfoliagein A and (-)-rhodomollein XXV, two highly oxygenated grayanoids featuring a synthetically challenging oxa-tricyclo[3.3.1.03.7]nonane 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 bicyclo[3.3.0]octene unit to the highly functional bicyclo[3.2.1]octane ring system and PPTS mediated procedure for converting (-)-mollfoliagein A to (-)-rhodomollein XXV.