The pigments of ‘dragon's blood’ resin. Part VIII. Synthesis of (±)-dracorubin and of (±)-nordracorubin

Abstract

(±)-Dracorubin (3,4-dihydro-5-methoxy-8-methyl-2,12-diphenyl-2H-dipyrano[2,3-a:2′,3′,4′-kl]xanthen-9-one) has been synthesised. Condensation of 7-benzyloxy-5-methoxy-6-methylflavan-4-ol with 7-hydroxy-5-methoxyflavan gave 7-benzyloxy-4-(7-hydroxy-5-methoxyflavan-8-yl)-5-methoxy-6-methylflavan, which was successively acetylated, debenzylated, and oxidised to 4-(7-acetoxy-5-methoxyflavan-8-yl)-5-methoxy-6-methyl-2-phenyl-1-benzopyran-7-one. Cyclisation of this anhydro-base with sodium methylsulphinylmethanide gave (±)-dracorubin. (±)-Nordracorubin has been synthesised similarly.