Design, synthesis, and structure of alkyl 1 H -pyrazolecarboxylates from a raspberry ketone methyl ether
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Design, synthesis, and structure of alkyl 1H-pyrazolecarboxylates from a raspberry ketone methyl ether Taís B. Goulart1, Adriana M. Neves1, Mayara S. P. Soares2, Francieli M. Stefanello2, Patrick T. Campos3, Sidnei Moura4, Roberta Cargnelutti5, Alex F. C. Flores1* 1
School of Chemistry and Food, Federal University of Rio Grande, Rio Grande 96203-900, RS, Brazil; e-mail: [email protected] 2 Laboratory of Biomarkers, Center for Chemical, Pharmaceutical and Food Sciences, Federal University of Pelotas, Capão do Leão 96010-900, RS, Brazil; e-mail: [email protected] 3 Laboratory of Synthetic, Structural and Computational Organic Chemistry, Sulriograndense Federal Institute (IFSul), Pelotas 96015-360, RS, Brazil; e-mail: [email protected] 4 Biotechnology Institute, University of Caxias do Sul, Caxias do Sul 95070-560, RS, Brazil; e-mail: [email protected] 5 Chemistry Department, Federal University of Santa Maria, Santa Maria 97105-900, RS, Brazil; e-mail: [email protected] Published in Khimiya Geterotsiklicheskikh Soedinenii, 2020, 56(10), 1314–1320
O Cl3C
O
, 65–180°C 20–24 h, 20–75%
OMe +
NH2NH2·HCl
Submitted June 17, 2020 Accepted after revision September 30, 2020
ROH
or OMe MW, 85–160°C 35 min, 33–80%
OR MeO
N H
N
R = Me, Et, n-Pr, i-Pr, i-Bu, i-Am, hexadecyl
This paper reports a one-pot synthesis of 5-[2-(4-methoxyphenyl)ethyl]-1H-pyrazole-3-carboxylates via cyclocondensation of 1,1,1-trichloro-4-methoxy-6-(4-methoxyphenyl)hex-3-en-2-one with hydrazine hydrochloride in ROH (R = Me, Et, n-Pr, i-Pr, i-Bu, i-Am, hexadecyl) under conventional and microwave heating. Yields are comparable in both methods, but under MW heating the reaction proceeds faster. The antioxidant activity of the compounds was measured using DPPH radical scavenging assay. It was observed, that the increase of the alcohol chain length decreases the antioxidant potential of the raspberry ketone derived molecular system. Keywords: 4-alkoxy-1,1,1-trichloroalk-3-en-2-ones, 1H-pyrazolecarboxylates, raspberry ketone, antioxidants, microwave irradiation.
1H-Pyrazole is a very important structural motif, attracting much attention in organic synthesis, medicinal chemistry, and agrochemistry.1 Among 1H-pyrazoles, 3- or 5-carboxylates have important applications as antiinflammatory and antioxidant agents.2 A versatile and interesting synthetic methodology using 1,1,1-trichloro4-methoxyalk-3-en-2-ones to produce 1H-pyrazolecarboxylates has been developed as one-pot process, when both [C–C–C + N–N] cyclization and hydrolysis of the trichloromethyl group to the carboxyl one occur. Using the acetal acylation reaction, it is possible to design the dielectrophilic 1,1,1-trichloro-4-methoxy-3-alken-2-one by selecting the respective alkyl methyl ketone precursor.3,4 Followed by the cyclocondensation reaction with hydrazine the choice of the alcohol as a solvent and reactant will 0009-3122/20/56(10)-1314©2020 Springer Science+Business Media, LLC
define the molecular structure of the alkyl 1H-pyrazolecarboxylate ob
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