Competitive cyclisation of singlet and triplet nitrenes. Part 7. Reaction pathways of 2-azidophenyl benzothienyl azides

Abstract

The thermal decomposition of 2-azidophenyl 2-(3-methylbenzo[b]thienyl) sulphide (7b) and 2-azidophenyl 3-(2-methylbenzo[b]thienyl) sulphide (8) proceeds efficiently by way of a spiro-benzothiazoline (9) or (10) giving benzothiopheno-benzothiazines (11) and (16) in both cases. From the former azide were also isolated two 2-benzothiophenylbenzothiazoles (12) and (13). The reactions do not proceed well in the absence of methyl substituents. 2-Azidophenyl 3-(2,5-dimethylthienyl) sulphide (19) surprisingly gave 2-methylbenzothiazole on thermolysis. These various reaction pathways have been rationalised by comparison with those of the related thienyl sulphides.