Enantioselective Synthesis of Cassane‐Type Furanoditerpenoids: Total Synthesis of Sucutiniranes C and D

Abstract

The first enantioselective total synthesis of cassane‐type furanoditerpenoids featuring an aromatic C ring and a substituted B ring is presented. The strategy employed relied on diastereoselective Diels–Alder (DA) reaction of an enantiomerically pure 1,3,3‐trisubstituted‐2‐vinyl‐cyclohexene (sterically demanding diene). It was secured in > 99 % ee through elaboration of enzymatically resolved 3‐ethoxy‐6‐(hydroxymethyl)‐6‐methyl‐cyclohex‐2‐en‐1‐one. Employing hexafluoro‐2‐propanol (HFIP) as the solvent, its DA cycloaddition onto benzo[b]furan‐4,7‐dione proceeded with exquisite endo‐selectivity under ambient temperature and pressure. Subsequent diastereo‐ and regio‐selective methyl Grignard addition provided a pivotal intermediate featuring the complete vouacapane framework. Its versatility and intriguing reactivity were demonstrated by conversion to sucutiniranes C and D.