Da. Klumpp et al., PREPARATION OF 3,3-DIARYLOXINDOLES BY SUPERACID-INDUCED CONDENSATIONSOF ISATINS AND AROMATICS WITH A COMBINATORIAL APPROACH, Journal of organic chemistry, 63(13), 1998, pp. 4481-4484
3,3-Diaryloxidoles are prepared in high yields (62-99%) by reaction of
isatin or substituted isatins with aromatics in triflic acid. The rea
ction shows a significant dependence on acid strength which suggests t
he formation of diprotonated, superelectrophilic intermediates. Reacti
on of isatin, benzene, and acid systems of varying strength (composed
of CF3SO3H and CF3CO2H) showed that the acid strength must be more aci
dic than H-0 = -11.5 for complete conversion to product. Reaction of i
satins with mixtures of aromatics allows for the preparation of librar
ies of 3,3-diaryloxindole products by combinatorial synthesis.