On the Microwave-Assisted Synthesis and Oxidation of Biginelli Compounds: Comparative Study of Dihydropyrimidinones and Thiones Oxidation

ISSN: 2213-3364 (Online)
ISSN: 2213-3356 (Print)


Volume 1, 2 Issues, 2014






Current Microwave Chemistry

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On the Microwave-Assisted Synthesis and Oxidation of Biginelli Compounds: Comparative Study of Dihydropyrimidinones and Thiones Oxidation

Author(s): Marta Pineiro, Bruno F.O. Nascimento, António M.d'A. Rocha Gonsalves, Sandra C.C. Nunes and Alberto A.C.C. Pais

Affiliation: Department of Chemistry, University of Coimbra, Rua Larga 3004-535, Coimbra, Portugal.

Abstract

A small library of twenty-two 3,4-dihydropyrimidin-2(1H)-ones and twenty-one thiones was synthesized under microwave irradiation using acetic acid as both solvent and catalyst. The oxidation of 3,4-dihydropyrimidin-2(1H)-ones to the corresponding pyrimidin-2(1H)-ones was systematically studied with heterogeneous and homogeneous oxidants. Microwave- assisted oxidation using potassium peroxydisulfate in an acetonitrile/water mixture at 100°C for 10 minutes produced the desired compounds in high yields for the majority of the 3,4-dihydropyrimidin-2(1H)-ones used. The decrease in the reaction yield observed in the case of 3,4-dihydropyrimidin-2(1H)-ones with bulky substituents at the C4 position was rationalized resorting to theoretical calculations. The oxidation of 3,4-dihydropyrimidine-2(1H)-thiones was also extensively studied. Using potassium peroxydisulfate or other powerful oxidants, such as oxone or hydrogen peroxide, pyrimidine-2(1H)-thione was not observed. However, evidence for the formation of this compound was obtained using 2,3-dichloro-5,6-dicyanobenzoquinone as oxidant under microwave irradiation. Electronic structure calculations indicate the stability of the 1,4-dihydropyrimidinethiol tautomer, which is deemed responsible for the different reactivity of these compounds.




Keywords: 1, 4-dihydropyrimidine, 1, 4-dihydropyrimidinethiol, 3, 4-dihydropyrimidin-2(1H)-ones, 3, 4-dihydropyrimidine- 2(1H)-thiones, biginelli, dihydropyrimidines, electronic calculation, microwave, monastrol, oxidation, potassium peroxydisulfate, pyrimidin-2(1H)-ones, pyrimidine-2(1H)-thiones, synthesis, tautomers.

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Article Details

Volume: 1
Issue Number: 2
First Page: 119
Last Page: 134
Page Count: 16
DOI: 10.2174/2213335601666140422225203
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