Homolytic aromatic substitution by heterocyclic free radicals. Part II. Reaction of thiazol-2-yl and benzothiazol-2-yl radicals with aromatic compounds

Abstract

Free-radical aromatic substitution by thiazol-2-yl radicals was carried out with variously substituted aromatic compounds. The thiazol-2-yl radical was generated by photolysis of 2-iodothiazole, or by thermal decomposition of the diazonium salt of 2-aminothiazole. The isomeric ratios and the relative rates of substitution were determined and compared with those obtained with phenyl radicals. These data confirmed the electrophilic character of the radical. The major by-products in the photolysis were identified as 3-arylisothiazoles from rearrangement of 2-arylthiazoles. Results describing the free-radical benzothiazolylation of alkylbenzenes (R = Me, Et, Prⁱ, and Bu^t) are also reported. From these results the benzothiazol-2-yl radical appears to be more electrophilic than the thiazol-2-yl radical.