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Open AccessArticle

Highly Efficient Synthesis of Substituted 3,4-Dihydropyrimidin-2-(1H)-ones (DHPMs) Catalyzed by Hf(OTf)4: Mechanistic Insights into Reaction Pathways under Metal Lewis Acid Catalysis and Solvent-Free Conditions

Jiangxi Key Laboratory of Organic Chemistry, Jiangxi Science and Technology Normal University, 605 Fenglin Avenue, Nanchang 330013, Jiangxi, China
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Academic Editor: Romano V. A. Orru
Molecules 2019, 24(2), 364; https://doi.org/10.3390/molecules24020364
Received: 2 January 2019 / Revised: 15 January 2019 / Accepted: 18 January 2019 / Published: 21 January 2019
(This article belongs to the Special Issue Advances in One-Pot Reaction)
In our studies on the catalytic activity of Group IVB transition metal Lewis acids, Hf(OTf)4 was identified as a highly potent catalyst for ”one-pot, three-component” Biginelli reaction. More importantly, it was found that solvent-free conditions, in contrast to solvent-based conditions, could dramatically promote the Hf(OTf)4-catalyzed formation of 3,4-dihydro-pyrimidin-2-(1H)-ones. To provide a mechanistic explanation, we closely examined the catalytic effects of Hf(OTf)4 on all three potential reaction pathways in both “sequential bimolecular condensations” and “one-pot, three-component” manners. The experimental results showed that the synergistic effects of solvent-free conditions and Hf(OTf)4 catalysis not only drastically accelerate Biginelli reaction by enhancing the imine route and activating the enamine route but also avoid the formation of Knoevenagel adduct, which may lead to an undesired byproduct. In addition, 1H-MMR tracing of the H-D exchange reaction of methyl acetoacetate in MeOH-d4 indicated that Hf(IV) cation may significantly accelerate ketone-enol tautomerization and activate the β-ketone moiety, thereby contributing to the overall reaction rate. View Full-Text
Keywords: hafnium triflate; 3,4-dihydropyrimidin-2-(1H)-ones; solvent-free; Biginelli reaction; mechanism hafnium triflate; 3,4-dihydropyrimidin-2-(1H)-ones; solvent-free; Biginelli reaction; mechanism
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MDPI and ACS Style

Kong, R.; Han, S.-B.; Wei, J.-Y.; Peng, X.-C.; Xie, Z.-B.; Gong, S.-S.; Sun, Q. Highly Efficient Synthesis of Substituted 3,4-Dihydropyrimidin-2-(1H)-ones (DHPMs) Catalyzed by Hf(OTf)4: Mechanistic Insights into Reaction Pathways under Metal Lewis Acid Catalysis and Solvent-Free Conditions. Molecules 2019, 24, 364. https://doi.org/10.3390/molecules24020364

AMA Style

Kong R, Han S-B, Wei J-Y, Peng X-C, Xie Z-B, Gong S-S, Sun Q. Highly Efficient Synthesis of Substituted 3,4-Dihydropyrimidin-2-(1H)-ones (DHPMs) Catalyzed by Hf(OTf)4: Mechanistic Insights into Reaction Pathways under Metal Lewis Acid Catalysis and Solvent-Free Conditions. Molecules. 2019; 24(2):364. https://doi.org/10.3390/molecules24020364

Chicago/Turabian Style

Kong, Rui; Han, Shuai-Bo; Wei, Jing-Ying; Peng, Xiao-Chong; Xie, Zhen-Biao; Gong, Shan-Shan; Sun, Qi. 2019. "Highly Efficient Synthesis of Substituted 3,4-Dihydropyrimidin-2-(1H)-ones (DHPMs) Catalyzed by Hf(OTf)4: Mechanistic Insights into Reaction Pathways under Metal Lewis Acid Catalysis and Solvent-Free Conditions" Molecules 24, no. 2: 364. https://doi.org/10.3390/molecules24020364

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