On the Tautomerism of 2,4-Disubstituted Thiazolones

Abstract

Four series of thiazolones − 2-phenyl-, 2-ethyl, 2-ethoxy, and 2-(ethylthio)thiazol-5-ones − have been synthesized. The tautomeric behavior of these thiazolones is discussed, and

Catalyst-Free Synthesis of Polysubstituted 5-Acylamino-1,3-Thiazoles via Hantzsch Cyclization of α-Chloroglycinates

“…Some of them existed in solution as mixtures of keto ( 10 ) and enol ( 4 ) tautomers (NMR). The keto form exhibited a diagnostic 3 J coupling between the C-5 and the NH protons (≈7.4 Hz), consistent with literature values in related systems [50]. The enol form may be the dominant/exclusive tautomer present in the solid state, as suggested by the broad OH signal observed in the FT-IR spectrum (see Supplementary Materials).…”

Chiral Phosphoric Acid Catalyzed Diastereo- and Enantioselective Mannich-Type Reaction between Enamides and Thiazolones

“…One of the most efficient methods is the enantioselective Mannich-type reaction of imines with α-amino acid derivatives as pronucleophiles to form a carbon–carbon bond, as well as vicinal stereogenic centers, in a single step. Among various pronucleophiles, azlactones and their sulfur analogues, thiazolones, are attractive synthons as α-amino acid derived pronucleophiles. Several studies have reported the efficient syntheses of α,β-diamino acid equivalents by enantioselective Mannich-type reactions between imines and azlactones , or thiazolones .…”

NMR Spectroscopic Study of Tautomerism in Solution and in the Solid State

“…Thus, concerning the enol-enol equilibria, indirect NMR information (blocked reference compounds, computed structures) ought to be employed. The remaining information to examine the fast chelate enol-enol tautomerism was collected by Koltsov In the tautomeric equilibrium of 2,4-disubstituted thiazolones, already well studied [30], in addition to the enol and a zwitterionic form, the existence of a second keto tautomer 14b (Scheme 5.10) was proved by NMR spectroscopy. The tautomers were identified by long-range H,H couplings across five bonds which are characteristic for the two tautomers [14a: 5 J(H-5,CH 2 (CH 3 ) and 14b: 5 J(H-2,CH 2 (Ph)]; these and other long-range n J(H,H) coupling constants were analyzed with the peak-top-fitting procedure of the deconvolution program of the PERCH software [31].…”