On the optical activity of the 3-aryl-4-hydroxycoumarin isolated from Millettia griffoniana:: molecular modelling and total synthesis

Semi-empirical calculations on 4-hydroxy-3-(3',4'-methylenedioxyphenyl)-5,6,7-trimethoxycoumarin, a natural product recently isolated from Millettia griffoniana, show low rotational barriers for the C(3)-C(1') bond (19.9 kJ mol(-1)) and for the inversion of the out-of-plane central 6-methoxy group (9.7 kJ mol(-1)). The structure of this compound is confirmed by its synthesis in 4 steps from 3,4,5-trimethoxyphenol in 37% overall yield, the key step being the ligand-coupling reaction of the 4-hydroxycoumarin 9 with 3,4-methylenedioxyphenyllead triacetate.