Regio- and stereoselective oxidation of flavan-3-ol-, 4-arylflavan-3-ol-, and biflavanoid derivatives with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ)

Article abstract of DOI:10.1016/S0040-4020(01)82322-X

The phenolic methyl esthers of flavan-3-ols, 4β-arylflavan-3-ols, and (-)-fisetinidol-(4β,8)-(+)-catechin biflavanoids are susceptible to regio- and stereoselective methoxylation at C-4 in moderate yields with DDQ in CHCl₃-MeOH solution. The observed asymmetric induction with exclusive formation of 2,4-trans products is compatible with the intermediacy of a diastereogenic donor-acceptor interaction, DDQ acting as the acceptor and oxidant. The 4-funtionalized analogues are of both synthetic and degradative significance in condensed tannin chemistry.