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 degrees 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 degrees 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.

TiCl(4)-induced Baylis-Hillman reactions of alpha,beta-unsaturated carbonyl compounds with aldehydes yield the (Z)-2-(chloromethyl)vinyl carbonyl compounds 5, which react with 1,4-diazabicyclo[2.2.2]octane (DABCO), quinuclidine, and pyridines to give the allylammonium ions 6. Their combination with less than one equivalent of the potassium salts of stabilized carbanions (e.g. malonate) yields methylene derivatives 8 under kinetically controlled conditions (S(N)2' reactions). When more than one equivalent of the carbanions is used, a second S(N)2' reaction converts 8 into their thermodynamically more stable allyl isomers 9. The second-order rate constants for the reactions of 6 with carbanions have been determined photometrically in DMSO. With these rate constants and the previously reported nucleophile-specific parameters N and s for the stabilized carbanions, the correlation log k (20 degrees C)=s(N + E) allowed us to calculate the electrophilicity parameters E for the allylammonium ions 6 (-19 < E < -18). The kinetic data indicate the S(N)2' reactions to proceed via an addition-elimination mechanism with a rate-determining addition step.

Baylis--Hillman Adducts. -The reaction of allylammonium ions with less than 1 equiv. of the potassium salts of stabilized carbanions affords methylene derivatives under kinetially controlled conditions (SN2' reactions). When more than 1 equiv. of the carbanions is used, a second SN2' reaction converts the methylene compounds into their thermodynamically more stable allyl isomers. The electrophilicity parameters are calculated for the allylammonium ions. The kinetic data indicate the SN2' reactions to proceed via an addition-elimination mechanism with the rate determining addition step. -(BAIDYA, M.; REMENNIKOV, G. Y.; MAYER, P.; MAYR*, H.; Chem. Eur. J. 16 (2010) 4, 1365-1371; Fachbereich Chem. Biochem.,