Synthesis of dixanthones and poly(dixanthone)s by cyclization of 2-aryloxybenzonitriles in trifluoromethanesulfonic acid

[GRAPHICS] Condensation of 2-fluorobenzonitriles with phenoxides affords 2-aryloxybenzonitriles that cyclize cleanly in trifluoromethanesulfonic acid at room temperature to give xanthone-iminium triflates, The C=N bond in these compounds is remarkably resistant to hydrolysis, but prolonged reaction with strong aqueous acid under vigorous conditions affords xanthones in good yield. The synthesis is exemplified for a novel series of polynuclear dixanthones and for a high molar mass polyxanthone derived from the previously unreported monomer 3,3 ' -difluoro-4,4 ' biphenyldicarbonitrile.