Constituents of dragon's blood. Part II. Structure and oxidative conversion of a novel secobiflavonoid
Abstract
A novel secobiflavonoid, (2S)-8-trans-[2-(6-benzoyloxy-4-hydroxy-2-methoxy-3-methylphenyl)ethenyl]-5-methoxyflavan-7-ol (1a) has been isolated from the resin dragon's blood, and identified by spectra and degradative experiments. Oxidation of (1a) or its derivatives with dichlorodicyanobenzoquinone or silver oxide occurs with ring closure to give new substituted arylfuro[2,3-h]benzopyrans or 8-(benzofuran-2-yl)flavans. Oxidation of the furobenzopyran (9b) with hydrogen peroxide–alkali converts the 2-methylphloroglucinol unit into a cyclopent-4-ene-1,3-dione ring.