Abstract
An easy and efficient copper-catalyzed reaction for the synthesis
of polysubstituted pyrazoles from phenylhydrazones and dialkyl ethylenedicarboxylates
is described. This reaction can tolerate a range of functionalities,
and the corresponding adducts can be obtained in moderate to good
yields.
Key words
heterocycles - copper catalysis - hydrazones - dialkyl ethylenedicarboxylates - pyrazoles
References and Notes
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Typical Procedure
for the Synthesis of Pyrazoles
An oven-dried reaction
tube was charged with CuI (3.8 mg, 0.02 mmol), NaOAc (16.4 mg, 0.20
mmol), benzaldehyde phenylhydrazone (1a,
47.0mg, 0.24 mmol), and dimethyl acetylenedicarboxylate (2a, 28.4mg, 0.20 mmol). Then DME (2 mL)
was added to the reaction system. The mixture was stirred at r.t.
for 2 h. After removal of the solvent under reduced pressure, the
crude product was purified by column chromatography on silica gel
(EtOAc-PE, 1:8) to give 3aa (49.0
mg, 73%) as white solid (Table
[²]
, entry 1); mp 152-154 ˚C. ¹H
NMR (400 MHz, CDCl3): δ = 7.75 (dd, J = 7.4, 1.8
Hz, 2 H), 7.54 (dd, J = 8.2,
1.4 Hz, 2 H), 7.50-7.40 (m, 6 H), 3.85 (s, 3 H), 3.82 (s,
3 H). ¹³C NMR (100 MHz, CDCl3): δ = 163.37,
160.64, 151.98, 139.03, 136.82, 131.33, 129.16, 129.06, 128.87,
128.77, 128.16, 124.53, 114.13, 53.11, 52.12. IR (neat): 2952, 1733,
1499, 1447, 1266, 911, 732 cm-¹. HRMS: m/z calcd for C19H16N2O4 [M + H]+: 337.1183;
found: 337.1175.
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