The preparation of thiazole-4- and -5-carboxylates, and an infrared study of their rotational isomers was written by Barton, Anne;Breukelman, Stephen P.;Kaye, Perry T.;Meakins, G. Denis;Morgan, David J.. And the article was included in Journal of the Chemical Society, Perkin Transactions 1 in 1982.Electric Literature of C8H10ClNO2S This article mentions the following:
A general procedure is reported for the preparation of thiazole-4- and -5-carboxylates containing alkyl and halo substituents. Treatment of Me2CHCHO and Cl2CHCO2Me with NaOMe in Et2O at 0掳, followed by addition of (H2N)2CS and 4 h reflux in MeOH gave the aminothiazole I. The thiazole II was prepared by treatment of EtO2CCHBrCOCMe3 with (H2N)2CS in refluxing EtOH for 1 h, followed by deamination with NaNO2-H3PO2. Both series of esters show IR carbonyl doublets caused by rotational isomerism; the more intense absorptions of the 4-carboxylates are at lower wave number, whereas those of the 5-carboxylates are the higher wave number component. In both series, the stronger bands arise from the thermochem. more stable forms. For the 4-carboxylates, these forms are the carbonyl O,S–syn-s-trans-rotamers. In the experiment, the researchers used many compounds, for example, Methyl 2-chloro-5-isopropylthiazole-4-carboxylate (cas: 81569-27-9Electric Literature of C8H10ClNO2S).
Methyl 2-chloro-5-isopropylthiazole-4-carboxylate (cas: 81569-27-9) belongs to thiazole derivatives. The higher aromaticity of thiazole is due to delocalization of a lone pair of sulfur electrons across the ring, which is evidenced by chemical shifts of ring hydrogen at 未 7.27 and 8.77 ppm (C2 and C4), indicating diamagnetic ring current. The pyridine-type nitrogen in the thiazole ring deactivates the ring for electrophilic substitution reactions, which is further reduced in acid due to protonation of the thiazole ring.Electric Literature of C8H10ClNO2S
Referemce:
Thiazole | C3H3NS – PubChem,
Thiazole | chemical compound | Britannica