Proton tautomerism and stereoisomerism in isomeric 4-(metoxyphenyl) amino-1,3-thiazol-2(5H)-one derivatives: Synthesis, crystal structure and spectroscopic studies

In this article, we have reported the most recent results of our systematic studies of phenyl-ring substituent effect on proton tautomerism and stereoisomerism in 4-phenylamino-1,3-thiazol-2(5H)-one derivatives. The work concerns the synthesis, analysis of 1H and 13C NMR and FT-IR spectra, and X-ray crystal studies of three isomeric compounds, i.e. 5-dimethylaminomethylidene-4-(o-,m-,p-methoxyphenyl)amino-1,3-thiazol-2(5H)-ones. All three isomers were found to solely exist in the amino tautomeric form, both in the DMSO solution and the solid phase. In the molecules of all the title compounds, the o-,m-,p-methoxyphenylamine residue has synperiplanar disposition with respect to the thiazolone system, while the 5-dimethylaminomethylidene residue adopts the Zconfiguration. DFT calculations correctly predict that the synperiplanar arrangement is favored in all investigated materials