he 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 1H and 13C 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 (13C and 15N) NMR spectroscopy.
Unambiguous structure determination of some pyrazolo [1,5‐a]pyrimidine derivatives by multinuclear NMR spectroscopy / Chimichi S.; Cosimelli B.; Bruni F.; Selleri S.. - In: MAGNETIC RESONANCE IN CHEMISTRY. - ISSN 0749-1581. - ELETTRONICO. - 30:(1992), pp. 1117-1121. [10.1002/mrc.1260301116]
Unambiguous structure determination of some pyrazolo [1,5‐a]pyrimidine derivatives by multinuclear NMR spectroscopy
Chimichi S.;Bruni F.;Selleri S.
1992
Abstract
he 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 1H and 13C 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 (13C and 15N) NMR spectroscopy.
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