Electrophilicity of 5-Benzylidene-1,3-dimethylbarbituric and -thiobarbituric Acids

The kinetics of reactions of acceptor-stabilized carbanions 2a−m with benzylidenebarbituric and
-thiobarbituric acids 1a−e has been determined in a dimethyl sulfoxide solution at 20 °C. Second-order
rate constants were employed to determine the electrophilicity parameters E of the benzylidenebarbituric
and -thiobarbituric acids 1a−e according to the correlation equation log k(20 °C) = s(N + E). With E
parameters in the range of −10.4 to −13.9, the electrophilicities of 1a−e are comparable to those of
analogously substituted benzylidenemalononitriles.