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SummaryActivated enol ethers derived from esters or the dinitrile of malonic acid, or from pentane-2,4-dione were treated with hydrazine hydrate. The structures of the obtained products – pyrazoles 5 – were studied with a focus on tautomerism and supramolecular structure. A reverse addition of the reagents led to the isolation of two novel products, namely bis-enehydrazines 6 with an unsymmetrical arrangement of the formally equivalent subunits.

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A set of 22 anilinomethylidene derivatives (13 new ones) of di(m)ethyl malonate, malononitrile and pentane-2,4-dione with various substituents in position 4- and 3-, respectively were prepared to study the characteristic influence of these substituents and solvents on chemical shifts in 13C NMR spectra and like reference compounds for kinetic measurements.

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There were studied series of activated enolethers (alkoxymethylene derivatives of malonic or 3-oxobutanoic acids derivatives of general formula R-O-CH=C(R 1 , R 2 ) where R 1 = R 2 / R 1 ≠ R 2 (R 1 , R 2 = CO 2 CH 3 , CO 2 CH 2 CH 3 , COCH 3 , CN) with N,N-dimethylhydrazine. They smoothly provided products of nucleophilic vinylic substitution reaction -dimethyl hydrazinyl methylene derivatives of malonic or 3-oxobutanoic acids (enhydrazines), respectively from 20 minutes to 2 hours at room temperature.

The kinetics and mechanism of the nucleophilic vinylic substitution of dialkyl (alkoxymethylidene)malonates (alkyl: methyl, ethyl) and (ethoxymethylidene)malononitrile with substituted hydrazines and anilines R 1 -NH 2 (R 1 : (CH 3 ) 2 N, CH 3 NH, NH 2 , C 6 H 5 NH, CH 3 CONH, 4-CH 3 C 6 H 4 SO 2 NH, 3-and 4-X-C 6 H 4 ; X: H, 4-Br, 4-CH 3 , 4-CH 3 O, 3-Cl) were studied at 25 C in methanol. It was found that the reactions with all hydrazines (the only exception was the reaction of (ethoxymethylidene)malononitrile with N,N-dimethylhydrazine) showed overall second-order kinetics and k obs were linearly dependent on the hydrazine concentration which is consistent with the rate-limiting attack of the hydrazine on the double bond of the substrate. Corresponding Brønsted plots are linear (without deviating N-methyl and N, N-dimethylhydrazine), and their slopes (b Nuc ) gradually increase from 0.59 to 0.71 which reflects gradually increasing order of the C-N bond formed in the transition state. The deviation of both methylated hydrazines is probably caused by the different site of nucleophilicity/basicity in these compounds (tertiary/secondary vs. primary nitrogen). A somewhat different situation was observed with the anilines (and once with N,N-dimethylhydrazine) where parabolic dependences of the kinetics gradually changing to linear dependences as the concentration of nucleophile/base increases. The second-order term in the nucleophile indicates the presence of a steady-state intermediate -most probably T AE . Brønsted and Hammett plots gave b Nuc = 1.08 and r = À3.7 which is consistent with a late transition state whose structure resembles T AE .