Total Synthesis of Schisanlactone A and Ganodermalactone H via Selective Transformation of a Cycloheptatriene Intermediate.

Herein we report the first total synthesis of schisanlactone A (1) and ganodermalactone H (2). The synthetic strategy features a domino [4 + 3] cycloaddition to construct a 7/6/5-membered ring system. This is followed by selective double-bond isomerization and then reduction of one of the three double bonds on the unsaturated seven-membered ring. Regio- and stereoselective reduction using SmI2 was key to construction of the challenging cycloheptadiene moiety. This approach provides a versatile foundation for the total synthesis of various seco-lanostane-type triterpenoids.