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Synthetic Communications
An International Journal for Rapid Communication of Synthetic Organic Chemistry
Volume 38, 2008 - Issue 20
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Original Articles

Simplified Approach to the Regiospecific Synthesis of Trichloromethylpyrazolines Using Microwave Irradiation

, , , , , & show all
Pages 3465-3476 | Received 26 Dec 2007, Published online: 30 Sep 2008
 

Abstract

Twelve novel 3-alkyl[aryl]-1-carboxamides-5-trichloromethyl-5-hydroxy-4,5-dihydro-lH-pyrazole have been synthesized in good yields (72–90%) using environmentally benign microwave-induced techniques. The compounds were synthesized from the cyclocondensation of 4-alkoxy-1,1,1-trichloro-3-alkyl[aryl]-2-ones [Cl3CC(O)C(R2) = C(R1)OR, where R = Me, Et; R1 = H, Me, Et, Pr, i-Pr, i-Bu, t-Bu, Ph, Ph-4-NO2, Ph-4-F, Ph-4-Cl, Ph-4-Br; and R2 = H, Me] with semicarbazide hydrochloride in the presence of pyridine and using methanol/water (3:1 v/v) as the solvent. The advantages of using microwave irradiation, rather than a conventional method, were demonstrated.

ACKNOWLEDGMENTS

The authors thank the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq, Contract Nos. 46.0804/00–6 and 480067/01-5), Fundação de Amparo à pesquisa do Estado do Rio Grande do Sul (FAPERGS), and Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) for financial support and fellowships. Also, the authors thank E. M. D. Flores (Departamento de Química, Universidade Federal de Santa Maria) for the providing the microwave equipment ETHOS 1 (Milestone Inc.) for the compound synthesis.

Notes

a Yields of isolated products.

b Reaction conditions: methanol/water (3:1 v/v), pyridine, 70 °C, MW, 100 W, 2.2 bar.

c Reaction conditions: methanol/water (3:1 v/v), 30–85 °C (2a–b, 2h–i, 2l; see Ref. 22).

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