Tandem Photoarylation–Photoisomerization of Halothiazoles: Synthesis, Photophysical and Singlet Oxygen Activation Properties of Ethyl 2‐Arylthiazole‐5‐carboxylates

Abstract

The photochemical reaction between ethyl 2-chlorothiazole-5-carboxylate and benzene gave no product. In contrast, the reaction with ethyl 2-iodothiazole-5-carboxylate gave ethyl 3-phenylisothiazole-4-carboxylate. The same behaviour was observed if the reaction was performed in the presence of furan, thiophene and 2-bromothiophene. The products thus obtained were studied for their photophysical properties and it was found that the observed absorptions [λ max =257 nm (ε = 7000 M -1 cm -1 ) for ethyl 3-phenylisothiazole-4-carboxylate, 278 nm (ε = 7000 M -1 cm -1 ) for ethyl 3-(2-furyl)isothiazole-4-carboxylate, 269 and 285 nm (ε = 7500 M -1 cm -1 ) for ethyl 3-(2-thienyl)isothiazole-4-carboxylate] are mainly due to π Ǟ π* transitions from the HOMO to the LUMO+1 orbital. The

Isothiazoles in the Design and Synthesis of Biologically Active Substances and Ligands for Metal Complexes

“…62 Among the methods for the synthesis of isothiazoles based on other heterocycles, the recently proposed method for the synthesis of 3-phenyl(heteroaryl)isothiazole-3-carboxylic acid ethyl esters 38a-d via the tandem photoarylation and photoisomerization of 2-iodothiazole-5-carboxylic acid ethyl ester 39 is of considerable interest (Scheme 19). 63 It should be noted that no rearrangement occurred in the case of a similar 2-chloro-substituted thiazole.…”