Flavan derivatives. XXX. Synthesis of racemic peltogynol trimethyl ether and its cis-cis-stereoisomer

Abstract

Synthesis of (±)-peltogynol trimethyl ether [(±)-trans-trans-7,6?,7?- tri-methoxyisochromano(4?,3?:2,3)chroman-4-ol and its (&)-cis-cis- stereoisomer are described. (+)-Peltogynol tetramethyl ether is shown to be the trans-trans-4,7,6?,7?-tetramethyl ether, and acid-catalysed etherification of the (±)-cis-cis-stereoisomer of peltogynol trimethyl ether with methanol is shown to yield the (±)-2,3-cis-3,4-trans- 4,7,6?,7?-tetramethyl ether. Oxidation of cis-cis-2?-hydroxymethyl- 7,4?,5?-trimethoxyflavan-3,4-diol with manganese dioxide gave 3(3?)- hydroxy-7,6?,7?-trimethoxyisochromano(4?,3?:2,3)chroman-4-one (a hemiacetal) and 2?-formyl-7,4?,5?-trimethoxyflavonol. Similar oxidation of trans-trans-2?-hydroxymethyl-7,4?,5?-trimethoxyflavan-3,4-diol gave minor quantities of the hemiacetal and 2?-formyl-7,4?,5?- trimethoxyflavonol, and yielded mainly the 2,3-trans-3-hydroxy- flavanone. N.m.r. data are presented for the compounds described.