Lablache-Combier studies

In addition to fragmentation on electron impact (Section 4.04.1.3.8), most of the references in this section involve photochemical studies and an excellent account of these has been given by Lablache-Combier (B-76PH123). 

The photoisomerization of isothiazole 5 to thiazole 6 (Scheme 3) was the first reported phototransposition in the isothiazole-thiazole heterocyclic system. Later work published during the period 1971 to 1978 by Lablache-Combier and co-workers, by Vernin and colleagues,"" andby Maeda and Kojima " also showed that methylisothiazoles phototranspose to methylthiazoles and that phenyl-substituted isothiazoles and thiazoles also undergo phototransposition reactions. A surprising finding, however, was that phenyhsothiazoles were not observed to react via the N2—C3 interchange pathway, an important pathway in pyrazole photochemistry. Furthermore, a common conclusion of these studies was that these photoisomerizations proceed by way of tricyclic zwitterionic intermediates, which had no counterparts in pyrazole photochemistry. 

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