Kinetics and Mechanism of the Addition of Benzylamines to Benzylidene Meldrum's Acids in Acetonitrile

Nucleophilic addition reactions of benzylamines <TEX>(XC₆H₄CH₂NH₂)</TEX> to benzylidene Meldrum's acids (BMA; <TEX>YC₆H₄CH=C(COO)₂C(CH₃)₂</TEX>) have been investigated in acetonitrile at 20.0 ℃. The rates of addition are greatly enhanced due to the abnormally high acidity of Meldrum's acid. The magnitudes of the Hammett <TEX>(ρX\;and\;ρY)</TEX> and Bronsted <TEX>(ρX)$</TEX> coefficients are rather small suggesting an early transition state. The sign and magnitude of the cross-interaction constant, <TEX>${ρ}XY$</TEX> (= -0.33), and kinetic isotope effects <TEX>$(k_H/k_D\;{}{~}{=}\;1.5-1.7)$</TEX> involving deuterated benzylamine nucleophilies <TEX>$(XC_6H_4CH_2ND_2)$</TEX> are indicative of hydrogen-bonded cyclic transition state. The activation parameters, <TEX>${Δ}H≠\;{}{~}{=}\;4\;kcal\;mol⁻¹\;and\;{Δ}S≠\;{}{~}{=}\;-37\;e.u.$</TEX>, are also in line with the proposed mechanism.