ChemInform Abstract: PHOTOUMLAGERUNG BEI HETEROCYCLEN 3. MITT. ARYLTHIAZOL‐ UND ARYLISOTHIAZOL‐ISOMERE, EXPERIMENTELLE ERGEBNISSE UND THEORETISCHE BETRACHTUNGEN

Abstract

Die Mengenverhältnisse der Photoisomeren (Thiazole und Isothiazole) bei UV‐Bestrahlung der 3 isomeren Phenylthiazole bzw. der 3 isomeren Phenylisothiazole in Gegenwart und Abwesenheit von Jod zeigen die selektive Wirkung von Jod.

Photochemistry of 3- and 5-Phenylisothiazoles. Competing Phototransposition Pathways

“…Vernin and Maeda previously reported that 3-phenylisothiazole (4) phototransposes to 4-phenylthiazole (2) , the expected P 6 permutation product, in ether or benzene solvent but not to 2-phenylthiazole (3) , the expected P 4 permutation product. − In our laboratory, two solutions of 3-phenylisothiazole (4) (3.0 mL, 2.0 × 10 -2 M) in benzene in the absence or presence of TEA (1.5 × 10 -2 M) were irradiated simultaneously for 3.0 h on a merry-go-round apparatus. GLC analysis showed that in the absence of TEA 34% of 3-phenylisothiazole (4) was consumed and that 4-phenylthiazole (2) and 2-phenylthiazole (3) were formed in 42.1% and 2.6% yields, respectively.…”

Properties and Reactions of Thiazole

“….rr-bond orders (calculated by the PPP method) between the ground state and the first excited state of the 2-phenylthiazole molecule and the free-valence numbers of the intermediate conjugate diradicals (Fig. 1-26) (493). The second pathway corresponds to the mechanism proposed by Kellog (494), which implies 180" rotations around the bonds adjacent to the sulfur atom.…”

Phototransposition Chemistry of 4-Substituted Isothiazoles. The P4 Permutation Pathway

“…By analogy with the known photochemistry of pyrazoles and isoxazoles, 4-substituted isothiazoles are expected to be the most reactive isothiazoles via the P 4 pathway. Despite this expectation, Vernin and colleagues irradiated 4-phenylisothiazole ( 1a ) in benzene solution but were unable to detect the formation of any phototransposition product . In our laboratory, when a solution of 1a in benzene was irradiated for 30 min, gas liquid chromatography (GLC) analysis showed that 82% of the reactant had been consumed and that 3% of the P 4 product, 4-phenylthiazole ( 2a ), had been formed.…”