Syntheses of (f)-7,8,4'-trimethoxyptew and (*t7-hydroxy-8,4'-dimetboxyptaocarpan have been carried out using the appropriate 2'-hydroxyisoflavones as intermediates and subjecting them to borohydride reduction followed by dehydrative cyclization.
THOUGH pterocarpin and homopteroca~i~ were discovered in 1874, the number of compounds beionging to this group and called pterocarpans was only eight up to last year. Harper et al.' isolated five more new compounds from the heartwood of Swartzia madagascariensis besides three known ones. Among them were four having oxygenation in the S-position which is a special feature since it is uncommona in their biogenetic precursors? the isoflavones. The simpier pterocarpans have been prepared in this laboratory using preferential deme~yla~on to produce ~-hydroxy~o~vone~K followed by reduction and dehydrative cyclization.6 With suitable modification this method has been used for the synthesis of racemates of two of the compounds isolated' namely 7,8,4'-trimethoxypterocarpan (I) and 7-hydroxy-8,4'-dimethoxypterocarpan (II).
The synthesis of 7,8,4'-trimetboxypterocarpapan (I) reported' has been achieved by the following route. Condensation of 2,4&nethoxyphenylacetic acid with pyrogallol in presence of zinc chloride furnished 2,3,4-trihydroxyphenyl-2,4&nethoxybeql ketone (IIIa) in good yield, while use of polyphosphoric acid gave poor yield. Hoeah condensation between 2,~e~ox~heny~a~to~t~e and pyrogallol gave poor yields of the ketone IIfa which was converted to 7,8,2~,4'-~~ethox~so~avone (IVa) by following two unambiguous routes. In one route, IIIa was partially methylated to