Unconventional Method for the Synthesis of 3-Carboxyethyl-4-formyl(hydroxy)-5-arylpyrazoles

Unconventional Method for Synthesis of 3-Carboxyethyl-4-formyl(hydroxy)-5-aryl-N-arylpyrazoles

Michael J. V. da Silva^†, Julia Poletto^†, Andrey P. Jacomini^†, Karlos E. Pianoski^†, Davana S. Gonçalves^†, Gessica M. Ribeiro^†, Samara M. de S. Melo^†, Davi F. Back^‡, Sidnei Moura^§, and Fernanda A. Rosa^*† 

^† Departamento de Química, Universidade Estadual de Maringá (UEM), 87030-900 Maringá, PR, Brazil

^‡ Departamento de Química, Universidade Federal de Santa Maria (UFSM), 97110-970 Santa Maria, RS, Brazil

^§ Instituto de Biotecnologia, Universidade de Caxias do Sul (UCS), 295070-560 Caxias do Sul, RS, Brazil

J. Org. Chem., 2017, 82 (23), pp 12590–12602

DOI: 10.1021/acs.joc.7b02361

Publication Date (Web): November 2, 2017

 

*E-mail: farosa@uem.br

Cite this:J. Org. Chem. 82, 23, 12590-12602

Abstract

An alternative highly regioselective synthetic method for the preparation of 3,5-disubstituted 4-formyl-N-arylpyrazoles in a one-pot procedure is reported. The methodology developed was based on the regiochemical control of the cyclocondensation reaction of β-enamino diketones with arylhydrazines.

Structural modifications in the β-enamino diketone system allied to the Lewis acid carbonyl activator BF₃ were strategically employed for this control. Also a one-pot method for the preparation of 3,5-disubstituted 4-hydroxymethyl-N-arylpyrazole derivatives from the β-enamino diketone and arylhydrazine substrates is described.

J. Org. Chem. 2017, 82, 12590

 

4-Formyl-N-arylpyrazole substrates occupy a prominent position in the field of organic synthesis since they are key intermediates in obtaining a wide range of biologically active compounds. Because of the synthetic versatility of the 4-formyl-N-arylpyrazole skeleton, their synthesis has been extensively explored. In an extension of their previously published research,

 

Rosa and co-workers at Universidade Estadual de Maringá described a one-pot synthetic method that regioselectively produced 3,5-disubstituted-4-formyl-N-arylpyrazoles . The β-enamino diketone starting materials were readily synthesized via published procedures. High regioselectivity was secured via the use of BF₃·OEt₂ as the carbonyl activator and a bulky amine as the enamine component. Acetonitrile proved to be the most suitable solvent for the reaction.

 

After an aqueous workup, the desired pyrazoles were obtained in excellent yields. A variety of functional groups were tolerated on the two aryl substituents. This operationally simple procedure afforded the 4-formyl-N-arylpyrazoles in high yields, regioselectively. Furthermore, the formyl group could be reduced in situ with sodium borohydride to generate the corresponding 4-hydroxymethyl-N-arylpyrazoles.

 

 

3-(Ethoxycarbonyl)-4-formyl-5-(4-nitrophenyl)-1-phenyl-1H-pyrazole (3a)

Light yellow solid; yield: 0.150 g (82%); mp 147.0–149.2 °C;

 

¹H NMR (300.06 MHz, CDCl₃) δ (ppm) 1.47 (t, 3H, J = 7.1 Hz, O–CH₂–CH₃), 4.54 (q, 2H, J = 7.1 Hz, O–CH₂-CH₃), 7.19–7.25 (m, 2H, Ph), 7.32–7.43 (m, 3H, Ph), 7.48 (d, 2H, J = 8.9 Hz, 4-NO₂C₆H₄), 8.19 (d, 2H, J = 8.9 Hz, 4-NO₂C₆H₄), 10.57 (s, 1H, CHO);

 

¹³C NMR (75.46 MHz, CDCl₃) δ (ppm) 14.4 (O–CH₂–CH₃), 62.3 (O-CH₂–CH₃), 122.0 (C4), 123.5 (4-NO₂C₆H₄), 125.9 (Ph), 129.5 (Ph), 129.6 (Ph), 131.8 (4-NO₂C₆H₄), 134.1 (4-NO₂C₆H₄), 137.8 (Ph), 143.5 (C5), 145.0 (C3), 148.4 (4-NO₂C₆H₄), 161.5 (COOEt), 186.6 (CHO);

 

HRMS (ESI+): calcd for C₁₉H₁₆N₃O₅⁺, [M+H]⁺: 366.1084, found 366.1101.

 

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