Geometrical Isomerism of Phenylhydrazones of α-Keto Esters. II. p-Substituted Phenylhydrazones of Ethyl Pyruvate and 2,4-Dinitrophenylhydrazones of Some α-Keto Esters

Abstract

Each geometrical isomer of various substituted phenylhydrazones of ethyl pyruvate and 2,4-dinitrophenylhydrazones of some α-keto esters was isolated in a pure state. Partial isomerizations of the E-isomers of the former hydrazones to the Z-isomers took place by keeping solutions of the hydrazones in organic solvents containing C, H, and Cl in the dark. An E- or Z-structure was assigned to each molecule on the basis of IR and 1H NMR spectra. In all cases, isomers with higher Rf-values on a silica gel TLC (using benzene as a developing solvent) involved an intramolecular hydrogen bonding between the imino hydrogen and the ester carbonyl oxygen. Thus, the Z-structure was assigned. An E-structure was assigned to other isomers with lower Rf-values. The present assignment is, thus, entirely the same as that proposed in a previous investigation.

Metal-Free Tandem Oxidative Cyclization for the Synthesis of 1,2-Dihydropyridazines and Pyrazoles

“…To our expectation, the desired coupling product 3a was obtained in 82% yield within 2 h (entry 1). From the downfield chemical shift of the N–H proton, 3a should have a Z-configuration . Other solvents such as dimethylformamide (DMF), CH 3 CN, CH 3 NO 2 , CHCl 3 , and 1,2-ClCH 2 CH 2 Cl (DCE) were also investigated (entries 2–6).…”

“…From the downfield chemical shift of the N−H proton, 3a should have a Zconfiguration. 12 Other solvents such as dimethylformamide (DMF), CH 3 CN, CH 3 NO 2 , CHCl 3 , and 1,2-ClCH 2 CH 2 Cl (DCE) were also investigated (entries 2−6). Both DCE and CH 2 Cl 2 were found to be the most suitable.…”

Solvent-Free, Continuous Synthesis of Hydrazone-Based Active Pharmaceutical Ingredients by Twin-Screw Extrusion

“…Control experiments were conducted (Table S2b, c) 38 that confirmed that heating alone was sufficient for the reaction to be initiated and proceed to completion. However, it must be noted that upon scale-up TSE is likely to be advantageous as it provides a means of intimately mixing the substrates as well as an even distribution of heat transfer.…”