Chemical studies on rotenoid. V. Synthesis of (-)-rotenone.

Abstract

A new synthesis of (-)-rotenone (1) has been accomplished. Decarboxylation and Vilsmeier formylation of (-)-tubaic acid (3) afforded (-)-tubaaldehyde (2) which was the key intermediate of (-)-rotenone synthesis. Condensation of 2 and Grignard reagent of phenyl 2-propynyl ether (5) and subsequent oxidation afforded (-)-1-(2, 3-dihydro-4-hydroxy-2-isopropenylbenzo[b]furan-5-yl)-4-(3, 4-dimethoxyphenoxy)-2-butyn-1-one (7). Thermal rearrangement of 7 gave (-)-6a, 12a-dehydrorotenol (8). 8 was smoothly converted to (-)-rotenone (1) in good yield by the treatment with weak bases such as pyridine or triethylamine in ethanol.