Oxidative cyclization of 1-(pyridin-2-yl)guanidine derivatives: a synthesis of [1,2,4]triazolo[1,5-a]pyridin-2-amines and an unexpected synthesis of [1,2,4]triazolo[4,3-a]pyridin-3-amines

Add time:07/12/2019    Source:sciencedirect.com

Oxidative cyclization of 1-(pyridin-2-yl)guanidine derivatives using N-chlorosuccinimide and aqueous potassium carbonate has been investigated. Chlorination of 1-(5-nitropyridin-2-yl)guanidine by N-chlorosuccinimide in methanol followed by addition of aqueous potassium carbonate gave rise to cyclization and afforded 6-nitro-[1,2,4]triazolo[1,5-a]pyridin-2-amine in one-pot. In the course of studying the scope and limitation of the reaction, it was found that some of the examined 1-(pyridin-2-yl)guanidine derivatives gave not only the desired [1,2,4]triazolo[1,5-a]pyridin-2-amines but also unexpected [1,2,4]triazolo[4,3-a]pyridin-3-amine products. As plausible reaction mechanisms of this oxidative cyclization, diazirine formation and nitrene formation are presented.

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