Chemistry of substituted pyrazolo[1,5-a] pyrimidines. Part 3. A structural correction of a pyrazolo[1,5-a][1,3]diazepine derivative on the basis of 13C NMR spectroscopy

Abstract

The reaction of 3-amino-4-cyanopyrazole (3) with ethyl 3-ethoxymethylene-2, 4-dioxopentanoate (4) has been reinvestigated and the nature of the condensation product firmly established. Ethyl 3-cyano-7-, methylpyrazolo[1, 5-a]pyrimidine-6-oxoacetate (1) and not, as formerly claimed, ethyl 3-cyano-7-methyl-6-oxopyrazolo[1,5-a][1,3]diazepine-8-carboxylate (2) is shown to be the final product in the reaction of ethyl 6-acetyl-3-cyanopyrazolo[1,5-a]pyrimidine-7-carboxylate (6) with aqueous acetic acid. The structure of 1 has been determined by ¹³C NMR spectroscopy and confirmed by independent synthesis.