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■ Coupling of Heteroaryldiazonium Tetrafluoroborates with 1,3-Dicarbonyl Compounds—regioselective Synthesis of Alkyl 1-Heteroaryl-4-hydroxy-1H-pyrazole-3-carboxylates

Simon Recnik, Jurij Svete,* and Branko Stanovnik

*Faculty of Chemistry and Chemical Technology, University of Ljubljana, Askerceva 5, P.O. Box 537, SLO-1000 Ljubljana, Slovenia

Abstract

Coupling of 1-cyano-4-oxo-4H-quinolizine- (2), 1-ethoxycarbonyl-4-oxo-4H-quinolizine- (3), and 4-oxo-4H-pyridino[1,2—b]pyrimidine-3-diazonium tetrafluoroborates (4) with 1,3-dicarbonyl compounds (1a—i) afforded the corresponding hydrazones (5—7) in 55—96% yields. The orientation around the C=N double bond in unsymmetrically substituted hydrazones (7a,c) was determined by NMR (NOESY) spectrometry. Heating of hydrazones (5a,b—7a,b), derived from alkyl 4-chloro-3-oxobutanoates (1a,b), furnished 1-(1-substituted quinolizin-3-yl)- (8, 9) and 1-(pyridino[1,2—a]-pyrimidin-3-yl)-4-hydroxy-1H-pyrazole-3-carboxylates (10) in 87—96% yields.