The pigments of ‘dragon's blood’ resin. Part VII. Synthesis of (±)-draconol, (±)-O-methyldraconol, (±)-O-methylisodraconol, and derivatives; the structure of dracorubin

Unequivocal syntheses of (±)-draconol (3,4-dihydro-9,11-dihydroxy-5-methoxy-8-methyl-2-phenyl-2H-pyrano-[2,3-a]xanthen-12-one), a major degradation product of the pigment dracorubin, and of (±)-O-methyldraconol and (±)-O-methylisodraconol are described. The structure of dracorubin (3,4-dihydro-5-methoxy-8-methyl-2,12-diphenyl-2H-dipyrano[2,3-a:2′,3′,4′-kl]xanthen-9-one) is thus uniquely defined. The oxidative coupling of 7-hydroxy-5-methoxyflavan with 7-hydroxy-6 (and 8)-methylflavylium chloride to yield 4-(7-hydroxy-5-meth-oxyflavan-8-yl)-6(and 8)-methyl-2-phenylbenzopyran-7-one is described.