In this paper, an efficient synthetic route from pyrazole-chalcones to novel 6-aryl-5-hydroxy-2-phenylpyrano[2,3-
c]pyrazol-4(2
H)-ones as 3-hydroxyflavone analogues is described. The methylation of 5-hydroxy-2,6-phenylpyrano[2,3-
c]pyrazol-4(2
H)-one with methyl iodide in the presence of a base yielded a compound containing a
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In this paper, an efficient synthetic route from pyrazole-chalcones to novel 6-aryl-5-hydroxy-2-phenylpyrano[2,3-
c]pyrazol-4(2
H)-ones as 3-hydroxyflavone analogues is described. The methylation of 5-hydroxy-2,6-phenylpyrano[2,3-
c]pyrazol-4(2
H)-one with methyl iodide in the presence of a base yielded a compound containing a 5-methoxy group, while the analogous reaction of 5-hydroxy-2-phenyl-6-(pyridin-4-yl)pyrano[2,3-
c]pyrazol-4(2
H)-one led to the zwitterionic 6-(
N-methylpyridinium)pyrano[2,3-
c]pyrazol derivative. The treatment of 5-hydroxy-2,6-phenylpyrano[2,3-
c]pyrazol-4(2
H)-one with triflic anhydride afforded a 5-trifloylsubstituted compound, which was further used in carbon–carbon bond forming Pd-catalyzed coupling reactions to yield 5-(hetero)aryl- and 5-carbo-functionalized pyrano[2,3-
c]pyrazoles. The excited-state intramolecular proton transfer (ESIPT) reaction of 5-hydroxypyrano[2,3-
c]pyrazoles from the 5-hydroxy moiety to the carbonyl group in polar protic, polar aprotic, and nonpolar solvents was observed, resulting in well-resolved two-band fluorescence. The structures of the novel heterocyclic compounds were confirmed by
1H-,
13C-,
15N-, and
19F-NMR spectroscopy, HRMS, and single-crystal X-ray diffraction data.
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