Synthesis of 2-nitroindoles via the Sundberg indole synthesis

Abstract

A three-step sequence has been developed for converting o-nitrobenzaldehydes into 2-nitroindoles. The key step involves the thermolysis of 2-(o-azidophenyl)nitroethylene (10) in xylenes which gives 2-nitroindole (4) in 54% yield, akin to the classic Sundberg indole synthesis. This procedure has also been utilized to synthesize 5,6-dimethoxy-2-nitroindole (14).