ChemInform Abstract: PHOTOCHEMISCHE ISOMERISIERUNG VON PHENYLTHIAZOLEN UND PHENYLISOTHIAZOLEN

Abstract

Bei UV‐Bestrahlung isomerisiert sich das Thiazol (I) zum Thiazol (II) und dem Isothiazol (III), wobei je nach den Reaktionsbedingungen (Lampen‐Typ) (II) oder (III) bevorzugt gebildet wird.

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

“…The assignment of transitions in the cases of 12 and 13 is similar to that of 11. Also in this case, the HOMOǞLUMO monoelectronic excitation is the main component of S 1 , but the transition to S 1 is not assigned to the experimental absorption peaks at 278 (12) and 285 nm (13) (Figure 2 and Table 4). In both 12 and 13, the intense absorption band is assigned to the transition to S 2 , which is mainly due to the HOMO Ǟ (LUMO+1) monoelectronic excitation, as in 11.…”

“…[8] Conclusive identification of the reaction product was obtained by performing a long-range HETCOR experiment. Assuming a C-4-5-H coupling constant of 3.5 Hz, [9] we observed a coupling between the signal at δ = 9.4 ppm in the 1 H NMR spectrum (the proton at C-5) and the signal at δ 129.6 ppm in the 13 C NMR spectrum (C-4). To confirm the isomerization reaction we prepared ethyl 2-phenylthiazole 5-carboxylate (15) through a Suzuki reaction between 9 and phenylboronic acid in the presence of [Pd 2 (dba) 3 ] (Scheme 5).…”

Thiazole Derivatives as Potential Chemotherapeutic Agents: Homolytic Arylation of Thiazole with Phenylazotriphenylmethane

“…5 Varian CH7. The chemical shift a t 7.49 ppm can be attributed to proton H, on C-4 (I), whereas it is found a t 7.86 ppm (31) in the unsubstituted thiazole. If the inductive effects of the electronegative substituents in the ring were considered by themselves, this absorption should take place at lower fields.…”

Photochemistry of Phenyl-Substituted 1,2,4-Thiadiazoles. 15N-Labeling Studies

“…This could result from direct fragmentation of the 3-phenyl-1,2,4-thiadiazole-2- 15 N ( 4 - 2- 15 N ) ring (Path A, Scheme ) leading to hydrogen cyanide and 15 N-labeled benzonitrile sulfide ( 15- 15 N ), which is known to eliminate sulfur to provide benzonitrile- 15 N ( 5- 15 N ) . Alternately, by analogy with isothiazole photochemistry, − photocleavage of the S−N bond 22 (Path B, Scheme ) would lead to diradical 16- 15 N , which would undergo cleavage to provide 5- 15 N and ultimately sulfur and hydrogen cyanide. Either pathway is consistent with the observation that photofragmentation of 4 - 2- 15 N yields only 5- 15 N .…”

“…The photochemical properties of 1,2,4-thiadiazoles 1 are intriguing because the ring can be viewed as a combination of an isothiazole 2 and a thiazole 3 . Although the photochemistry of isothiazoles and thiazoles has been extensively studied, − no accounts of the photochemistry of 1,2,4-thiadiazoles have appeared in the literature. We now report that phenyl-substituted 1,2,4-thiadiazoles undergo photofragmentation, phototransposition, and an unusual reaction leading to the formation of 1,3,5-triazines.…”