The conversion of (+)-catechin tetramethyl
ether into (-)-2-chloro-5,7,3',4'-tetramethoxyisoflavan is shown to proceed by
1,2-migration of the 2-aryl group with inversion of configuration at the
3-position of the flavan nucleus (the migration terminus). The chloroisoflavan
was converted into (+)-cis-2-acetoxy-5,7,3',4'-tetramethoxyisoflavan and
reduction of this gave (+)-2-(3,4-dimethoxyphenyl)-3-(2,4,6-trimethoxyphenyl)propan-1-ol.
This was converted into the corresponding (+)-propane which gave (-)-methylsuccinic
acid on ozonolysis. The (+)-propane therefore possesses the (8)-configuration
corresponding to the (S)-configuration of the (+)-2,3-diarylpropan-1-ol and the
(3s)-configuration of the (+)-cis-2-acetoxy-isoflavan. (+)-cis-2-Ethoxy- and
(+)-cis-2-methoxy-5,7,3',4'-tetramethoxyisoflavan have been converted into the
related (+)-1-alkoxy-2,3-diarylpropanes. Chlorination of the phloroglucinol
nucleus in (+)-catechin tetramethyl ether may occur during reaction with
phosphorus pentachloride and is shown to lead to
2,6-dichloro-5,7,3',4'-tetramethoxyisoflavan. Racemic cis- and laevorotatory
and racemic trans-2-acetoxy-5,7,3',4'-tetramethoxyisoflavan have been prepared.
Nuclear magnetic resonance and optical rotatory dispersion data for a number of
isoflavans are reported. The absolute configurations of pterocarpin,
homopterocarpin, and pisatin are inferred.
