Room-Temperature, Metal-Free, and One-Pot Preparation of 2H-Indazoles through a Mills Reaction and Cyclization Sequence

Abstract

The Mills reaction and cyclization of readily available 2-aminobenzyl alcohols and nitrosobenzenes using thionyl bromide provided 2H-indazoles in up to 88 % yields. In the metal-free process, acetic acid played a crucial role for the both Mills reaction and cyclization. A brominated 2H-indazole could also be obtained through the one-pot sequence.

Keywords: cyclization; indazole; metal-free synthesis; nitrogen heterocycles; one-pot reaction.