Proton tautomerism and stereoisomerism of 4-amino-1,3-thiazol-2(5H)-one derivatives bearing substituents with opposite electronic effects: Synthesis, structure and spectroscopic studies

Proton tautomerism and stereoisomerism in 5-[(dimethylamino)methylidene]-4-[3/4-(trifluoromethylphenyl)amino]-1,3-thiazol-2(5H)-ones: synthesis, crystal structure and spectroscopic studies

“…The results obtained for compounds 4 and 5, as well as for the previously described 5-[(dimethylamino)methylidene]-4-(phenylamino)-1,3-thiazolin-2-one (Pyrih et al, 2023a) and its o/m/p-hydroxyphenyl (Pyrih et al, 2023b) and o/m/p-meth- for p-, m-and o-H atoms, respectively), and chemical shifts (ppm) for the C (upper value) and H (lower value) atoms of (a) 4 and (b) 5. oxyphenyl (Pyrih et al, 2024) derivatives, reveal an exceptionally high persistence of the amine tautomeric form in 4-(phenylamino)-1,3-thiazol-2(5H)-one derivatives, and the lack of influence of substituents located at the arene ring, irrespective of their position and electron-withdrawing prop-erties, on the equilibrium of the amine-imine proton tautomerism.…”

“…3, and Figs. S1 and S5, and Tables S3 and S4 in the supporting information) were assigned to the N7 position based on a comparative analysis of 5-[(dimethylamino)methylidene]-4-(phenylamino)-1,3-thiazolin-2-one (� = 9.50 ppm) (Pyrih et al, 2023a) and its derivatives with -OH (� = 9.37 and 9.34 ppm, respectively) (Pyrih et al, 2023b) and -OCH 3 substituents (� = 9.51 and 9.42 ppm, respectively) (Pyrih et al, 2024) in the meta and para positions of the arene ring. The need to use this type of comparative analysis was dictated by the absence of amidine H-atom correlation signals in the two-dimensional (2D) 1 H, 13 C HMBC (heteronuclear multiple bond correlation) correlation spectrum (Figs.…”

“…With this article we continue our systematic studies of proton tautomerism in 4-anilinothiazolidinones. Previous works analyzed the impact of the electronic structure of the ylidene moieties (Pyrih et al, 2023a), as well as the substituent position around the arene ring (Pyrih et al, 2023b(Pyrih et al, , 2024. As the previously studied substituents were all electron-donating, we were also interested in creating and studying derivatives with an electron-withdrawing substituent, such as the trifluoromethyl group.…”

Proton tautomerism in 5-dimethylaminomethylidene-4-(o-,m-,p-hydroxyphenyl)amino-1,3-thiazol-2(5H)-ones: synthesis, crystal structure and spectroscopic studies

“…The hydrogen bonding energies of N7-H7Á Á ÁO6 i bonds in an analogous group of compounds, 5-dimethylaminomethylidene-4-phenylamino-1,3-thiazol-2(5H)-one (Pyrih et al, 2023), take similar values and are 3.53 (2-I) and 3.64 kcal mol À1 (2-II). For the present compounds 1-3, it is noted that the hydrogen bonding energy depends on the substitution of the phenyl ring.…”

“…at 9.08 and 9.84 ppm were assigned to positions N7 and O14, respectively, based on comparison with other related structures. Indeed, the signal at 9.08 ppm was found to correspond to the 8.96 ppm signal assigned to the H atom at the N7 position in 5-dimethylaminomethylidene-4-(2-methoxyphenyl)amino-1,3-thiazol-2(5H)-one [Pyrih (2023), unpublished); CCDC 2252019; Groom et al, 2016], whereas the signal at 9.84 ppm corresponded to the signals of 10.06 ppm for the H atom of the OH group in 4-(2-hydroxyphenyl)amino-1,3-thiazol-2(5H)-one (Pindela, 2020), and the signal at 9.95 ppm corresponded to the H atom of the OH group in 5-(4-chlorophenylmethylidene)-4-(2-hydroxyphenyl)amino-1,3thiazol-2(5H)-one (Kaminskyy et al, 2015).…”