Hm. Colquhoun et al., Synthesis of dixanthones and poly(dixanthone)s by cyclization of 2-aryloxybenzonitriles in trifluoromethanesulfonic acid, ORG LETT, 3(15), 2001, pp. 2337-2340
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Condensation of 2-fluorobenzonitriles with phenoxides affords 2-aryloxybenz
onitriles that cyclize cleanly in trifluoromethanesulfonic acid at room tem
perature to give xanthone-iminium triflates, The C=N bond in these compound
s is remarkably resistant to hydrolysis, but prolonged reaction with strong
aqueous acid under vigorous conditions affords xanthones in good yield. Th
e synthesis is exemplified for a novel series of polynuclear dixanthones an
d for a high molar mass polyxanthone derived from the previously unreported
monomer 3,3 ' -difluoro-4,4 ' biphenyldicarbonitrile.