Synthesis of dixanthones and poly(dixanthone)s by cyclization of 2-aryloxybenzonitriles in trifluoromethanesulfonic acid.
[reaction: see text] 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.
Colquhoun
H M
HM
Department of Chemistry, University of Manchester, Oxford Road, Manchester M13 9PL, UK. h.m.colquhoun@rdg.ac.uk
Lewis
D F
DF
Williams
D J
DJ