Furanosesquiterpenoids: Total Synthesis of Pallescensins 2, F, and G

Article abstract of DOI:10.1246/bcsj.56.491

Oxidation of the synthetic pallescensin 1 with m-chloroperbenzoic acid, follwed by treatment of the resulting epoxide with lithium diethylamide, afforded 3-<2-(2-furyl)ethyl>-4,4-dimethyl-2-methylenecyclohexanol (6).The alcohol 6 was dehydrated with refluxing hexamethylphosphoric triamide to give pallescensin 2.Oxidation of 6 with pyridinium chlorochromate, followed by intramolecular cyclization with 85percent phosphoric acid, afforded 5,5a,6,7,8,9,9a,10-octahydro-6,6-dimethyl-4H-benzo<5,6>cyclohepta<1,2-b>furan-9-one.This was converted into the corresponding α,β-unsaturated ketone (10) via an α-phenylseleno ketone.Reduction of 10 with lithium aluminium hydride, followed by dehydration with hexamethylphosphoric triamide at 200-210 deg C, afforded pallescensin G, which was further isomerized to pallescensin F.