A concise synthesis of a tetrahydropyrazolopyrazine building block

Abstract

A concise synthesis of a tetrahydropyrazolopyrazine building block is described. 5-Methyl-4,5,6,7-tetrahydropyrazolo[1,5-a]pyrazin-2-ylamine was prepared in three steps and 80% yield from 5-nitro-2H-pyrazole-3-carboxylic acid. This compound was then coupled with 4-bromo-6-chloro-2-methyl-2H- pyridazin-3-one in the presence of sodium tert-pentoxide to give the target product in 87% yield. The process was successfully scaled up to a multihundred gram scale. © 2012 American Chemical Society.