Methylisothiazoles undergo phototransposition in neutral solution to methylthiazoles by a single permutation process. Methylisothiazole-methylisothiazole transpositions, previously reported to occur, were not detected in these reactions. In trifluoroacetic acid solvent, protonated methylisothiazoles and methylthiazoles phototranspose by P4 and P5 permutation pathways, respectively, resulting in a unique phototransposition cycle.
