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Tandem Photoarylation–Photoisomerization of Halothiazoles: Synthesis, Photophysical and Singlet Oxygen Activation Properties of Ethyl 2‐Arylthiazole‐5‐carboxylates
Author(s) -
Amati Mario,
Belviso Sandra,
D'Auria Maurizio,
Lelj Francesco,
Racioppi Rocco,
Viggiani Licia
Publication year - 2010
Publication title -
european journal of organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 1434-193X
DOI - 10.1002/ejoc.201000096
Subject(s) - chemistry , carboxylate , isothiazole , photochemistry , singlet oxygen , singlet state , homo/lumo , medicinal chemistry , excited state , oxygen , stereochemistry , organic chemistry , molecule , physics , nuclear physics
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 → π* transitions from the HOMO to the LUMO+1 orbital. The tested compounds showed fluorescence [λ em = 350–400 (λ exc = 300 nm), 360 and 410 nm (λ exc = 320 nm), 412 nm (λ exc = 340 nm) for ethyl 3‐phenylisothiazole‐4‐carboxylate, 397 and 460 nm (λ exc = 300 nm), 381, 394 and 460 nm (λ exc = 320 nm), 381, 398 and 466 nm (λ exc = 340 nm) for ethyl 3‐(2‐furyl)isothiazole‐4‐carboxylate, 372, 377 and 414 nm (λ exc = 300, 320 and 340 nm respectively) for ethyl 3‐(2‐thienyl)isothiazole‐4‐carboxylate], possibly due to dual emission from different excited states. The use of the compound obtained as a sensitizer in the photo‐oxidation of trans ‐α,α′‐dimethylstilbene showed that all the new compounds are singlet‐oxygen sensitizers.