Synthesis of some pterocarpenes obtained from Brya ebenus

Abstract

The syntheses of bryacarpenes-1, -2, and -4, [4,10-dihydroxy-3,8,9-trimethoxy-(1), 10-hydroxy-3,8,9-trimethoxy-(2), and 4-hydroxy-3,9,10-trimethoxy-6H-benzofuro[3,2-c][1]benzopyran (3)], (±)-bryaflavan [(±)-3′,6,7-trihydroxy-2′,4′-dimethoxyisoflavan (33)], 4-hydroxy-3,7-dimethoxy-(18) and 3,7-dimethoxy-6H-benzofuro[3,2-c][1]benzopyran-9,10-quinone (19) is described. The quinones are not identical with bryaquinone and deoxybryaquinone, for which structures (18) and (19) had been proposed previously. In the syntheses of the pterocarpenes the novel reduction of isoflavones to isoflavan-4-ones by di-isobutylaluminium hydride was used.