Facile synthesis of rubiadin by microwave heating

Abstract

Rubiadin (4) (1,3-dihydroxy-2-methylan-thraquinone), which is one of the natural dyes from the roots of Rubiaceae, was synthesized from phthalic anhydride (1) and 2,6-dihydroxytoluene (3) by two reaction steps, that is, a Friedel-Crafts reaction with AlCl3 and a cyclization with H 2SO4/HBO2. Microwave heating resulted in remarkable acceleration of the reaction rate in the first reaction, and had an effect in reducing the reaction time and increasing the yield of rubiadin (4) in the second reaction. © The Japan Wood Research Society 2006.