Protonenresonanz-Untersuchungen an aromatischen Heterocyclen, II: Isothiazole und Isothiazolium-Ionen

Photochemistry of 3- and 5-phenylisothiazoles. Competing phototransposition pathways

5-Phenylisothiazole undergoes phototransposition via the electrocyclic ring closure-heteroatom migration pathway and by the N(2)-C(3) interchange reaction pathway. The latter route is enhanced by the addition of triethylamine (TEA) to the reaction medium and by increasing the polarity of the solvent. In addition to phototransposition, 5-phenylisothiazole also undergoes photocleavage to 2-cyano-1-phenylethenethiol which was trapped by reaction with benzyl bromide to yield 2-cyano-1-phenylethen-1-ylbenzyl thioether. 3-Phenylisothiazole also phototransposes by both reaction pathways, but the product distribution is not affected by the addition of TEA or by changing the solvent polarity.