Oxidation of Flavan-3-ols to 3-Oxoflavans

Abstract

3-Oxoflavan and 4?-methoxy-3-oxoflavan were prepared by Pfitzner- Moffatt oxidation of the corresponding trans-flavan-3-ols, but similar oxidation of 2,3-trans-7,8,3?,4?-tetramethoxyflavan-3-led to an inseparable mixture of 7,8,3?,4?-tetramethoxy-3-oxoflavan and 7,8,3?,4?-tetramethoxy-3-methylthiomethoxyflav-3-ene. Pyrolysis of 2,3- trans-3,4-cis-acetoxy-7,4?-dimethoxyflavan-3-ol led to formation of 7,4?-dimethoxy-3-oxoflavan and 2,3-tuans-3,4-cis-3-acetoxy-7,4?- dimethoxyflavan-4-ol(by migration of the acetyl group). N.m.r. data are recorded for the compounds obtained.