Intramolecular nitrene insertions into aromatic and heteroaromatic systems. Part II. Insertions into thiophen rings

Abstract

Thermal decomposition of 2-(2-azidobenzyl)thiophen (5) and of 2-(2-azidobenzyl)-5-methylthiophen (9) gives thieno[3,2-b]quinoline (14) and the 2-methyl derivative (19), respectively; in the former case a second major product was 1,2-dihydropyrrolo[1,2-a]indole-3-thione (17), obtained with a small amount of the corresponding 2-oxo-compound (18). Decomposition of 3-(2-azidobenzyl)-2,5-dimethylthiophen (13) gave 2,4-dimethylthieno[3,2-c]quinoline (22), with smaller amounts of 3-(2-aminobenzyl)-2,5-dimethylthiophen (12) and 2-methyl-3-propylquinoline (20). Mechanisms for these nitrene insertions are suggested; the thienoquinolines (14) and (22) have been synthesised by standard procedures.