Colouring matters of Australian plants. XXIII. A new synthesis of arylphenalenones and naphthoxanthenones

Condensation of naphthalene-2,7-diol with 2,4-dioxo-4-phenylbutanoic acid gives 6-hydroxy-1-oxo-9-phenyl-1H-phenalene-7-carboxylic acid which is readily converted into the lactone and on treatment with diazomethane forms only methyl 6-methoxy-1-oxo-9-phenyl-1H-phenalene-7- carboxylate. Analogous reactions of other 4-aryl-2,4-dioxobutanoic acids with naphthalene-2,7-diol or with 3,6-dimethoxynaphthalene-2,7- diol give easy access to arylphenalenones and naphthoxanthenones related to natural pigments.