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

The first enantioselective total synthesis of cassane-type furanoditerpenoids featuring an aromaticCring and a substitutedBring 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 exquisiteendo-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.