Condensed thiophen ring systems. Part XIII. Synthesis of azidobenzo[b]thiophens and their conversion into thienobenzoxazoles

Abstract

The preparation is reported of a series of azidobenzo[b]thiophens [(1)–(3), (5), (6), and (22)]. The 5-azides (2)–(5) gave the 2-methylthieno[2,3-g]benzoxazoles (7)–(10)(angular products) on thermolysis in a mixture of polyphosphoric and acetic acids. In contrast, similar treatment of 5-azidobenzo[b]thiophen 1,1-dioxide (6) gave the linear product, 2-methylthieno[3,2-f]benzoxazole 7,7-dioxide (11). 4-Azidobenzo[b]thiophen (1) underwent a Bamberger-type rearrangement under similar conditions, to give 4-acetamido-7-acetoxybenzo[b]thiophen (17).