The structure and synthesis of the novel orchid pigments dengibsin and dengibsinin

Abstract

The structures of the orchid pigments dengibsin and dengibsinin have been revised to 2,5-dihydroxy-4-methoxy-9H-fluoren-9-one (4) and 3,5-dihydroxy-2,4-dimethoxy-9H-fluoren-9-one (5). The synthesis of these compounds is described. It has been found that 2′-methoxybiphenyl-2-carboxylic acids, on treatment with trifluoroacetic anhydride or oxalyl chloride, undergo cyclization giving 6H-dibenzo[b,d]pyran-6-ones.