Unambiguous structure determination of some pyrazolo [1,5-a]pyrimidine derivatives by multinuclear NMR spectroscopy

✍ Scribed by Stefano Chimichi; Barbara Cosimelli; Fabrizio Bruni; Silvia Selleri

• Publisher: John Wiley and Sons
• Year: 1992
• Tongue: English
• Weight: 376 KB
• Volume: 30
• Category: Article
• ISSN: 0749-1581
• DOI: 10.1002/mrc.1260301116

✦ Synopsis

Abstract

The condensation of 3(5)‐aminopyrazole and 5‐amino‐3‐phenylpyrazole with ethyl 2,4‐dioxopentanoate and 2‐ethoxymethylidene‐3‐oxobutyrate has been re‐investigated. Contrary to previos reports, the former reaction gives rise to both regioisomeric pyrazolo [1,5‐a]pyrimidines (5‐carbethoxy‐7‐methyl‐and 7‐carbethoxy‐5‐methyl‐), the structures of which were determined by ^1^H and ^13^C NMR spectroscopy. The 6‐carbethoxy‐7‐methyl‐regioisomer is shown to be the only product in the reaction of the same aminopyrazoles with 2‐ethoxymethylidene‐3‐oxobutyrate; the regiochemical assignment was independently achieved by multimuclear (^13^C and ^15^N) NMR spectroscopy.