Colouring matters of the aphididae. Part XXVIII. A coupling reaction involving phenols and quinones. Reconstitution of the protoaphins, and synthesis of the chrysoaphin chromophore

Abstract

Certain water-soluble phenols and hydroxynaphthaquinones undergo oxidative coupling with one another on standing in neutral aqueous solution at room temperature. The process probably involves the former as an electron donor and the latter as an election acceptor. In this way the quinone A and glucoside B, derived from reduction of protoaphin-fb, recombine to form a mixture containing protoaphin together with larger amounts of a symmetrically coupled analogue. Further reactions of the latter are described. Quinone A also reacts similarly with naphthalene-1,8-diol to yield ultimately a product having the chromophore of the chrysoaphins. An analogous reaction between 5-hydroxy-1,4-naphthaquinone (juglone) and naphthalene-1,8-diol leads to 4,9-dihydroxyperylene-3,10-quinone. The process appears to be of wide applicability in synthetic and biogenetic studies on aphid pigments and in the synthesis of a variety of polycyclic systems.