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Theoretical and experimental investigation of the polyeletrophilic β-enamino diketone: straightforward and highly regioselective synthesis of 1,4,5-trisubstituted pyrazoles and pyrazolo[3,4-d]pyridazinones

da Silva, Michael J. V., Silva, Raí G. M., Melo, Ulisses Z., Gonçalves, Davana S., Back, Davi F., Moura, Sidnei, Pontes, Rodrigo M., Basso, Ernani A., Gauze, Gisele F., Rosa, Fernanda A.
RSC advances 2015 v.6 no.1 pp. 290-302
Lewis acids, aniline, electrospray ionization mass spectrometry, hydrazines, monitoring, nuclear magnetic resonance spectroscopy, pyrazoles, regioselectivity
Obtaining a new precursor enamino diketone with five electrophilic centers is reported, along with theoretical and experimental studies of its reactivity against mono- or dinucleophiles. The Fukui function showed that the β-carbon is the most electrophilic center, followed by the carbonyl ketone and the carbonyl ester, respectively. The reaction of enamino diketone with aniline and hydrazines allowed for the synthesis of a new enamino diketone and 1,4-disubstituted pyrazoles-5-carboxylates, respectively. The regiochemistry and mechanism of syntheses of 1,4-disubstituted pyrazoles-5-carboxylates were determined from reaction monitoring by ESI-MS, NMR analysis and crystallographic data, and fully agreed with the theoretical results. The versatility and efficiency of the enamino diketone was demonstrated by the reaction with hydrazines furnishing multi-functionalized pyrazoles and pyrazolo[3,4-d]pyridazinone derivatives with high regioselectivity.