Kinetic studies on the nucleophilic addition to double bonds. 1. Addition of amines to electrophilic carbon-carbon double bonds

Substituent electrophilicities in the NMR spectra of barbituric derivatives

“…Rate and equilibrium constants for the addition of amines to substituted 5-benzylidene barbituric acids have been measured in different solvents. [13,14] The obtained kinetic constants were found to correlate with s + constants, showing that the reactivity of the electrophilic double-bond of compounds 1 depended more strongly on the nucleophilicity of the X substituent than might be expected from their s values. This is a result of the well-known exalted through-resonance between para-substituents X and a conjugated double bond (Scheme 3) and should be observed in a comparison of the chemical shifts of the olefinic carbon atoms of substituted derivatives 1.…”

“…Kinetic data related with compounds 1 provide examples of this. Rate and equilibrium constants for the addition of amines to substituted 5‐benzylidene barbituric acids have been measured in different solvents . The obtained kinetic constants were found to correlate with σ + constants, showing that the reactivity of the electrophilic double‐bond of compounds 1 depended more strongly on the nucleophilicity of the X substituent than might be expected from their σ values.…”

“…In all proton spectra, the N-CH 3 signals appeared as two conspicuous singlets in the range d = 3.30-3.50 ppm. The 13 wileyonlinelibrary.com/journal/mrc tended to deshield the centers closer to it, and its field effect also was dependent on its distance from the center, decreasing with this distance. Thus, the effect of the benzylidene substituent on the carbonyl signals decreased in the order C-2 < C-4 < C-6.…”

“…To investigate these variations in a systematic way, we prepared a series of substituted N,N'-dimethylbarbituric derivatives 1 and compared their 1 H and 13 C NMR spectra, in search of correlations between the spectral data and global or group electrophilicities, obtained from theoretical calculations.…”

Retro‐Aldol Reaction of Retinylidene‐1,3‐Diketones; Correlation with Biological Activity

“…Retinylidene-1 ,3-diketones can be considered to be 'cryptic' Lewis acids similar to benzylidene Meldrum's acid and related compounds whose reaction with nucleophiles has been studied by Shuster et al [3] and by Bernasconi & Leonarduazi [4]. Benzylidene Meldrum's acid contains a C , C double bond which is extremely susceptible to nucleophilic attack, and it ultimately fragments to give the products…”