Mechanistic investigation inspired “on water” reaction for hydrobromic acid‐catalyzed Friedel–Crafts–type reaction of β‐naphthol and formaldehyde

Abstract

The mechanism of the HBr-catalyzed Friedel-Crafts-type reaction between β-naphthol and HCHO was investigated by DFT to improve this reaction. The HBr-H O co-catalyzed the preferential pathway undergoes the concerted nucleophilic addition and hydrogen shift, stepwise followed by H O elimination and the CC bond formation. The origin of the high catalytic activity of HBr is ascribed to CH···Br and OH···Br interactions, which suggest that the active species is Br . Moreover, water molecules efficiently assist in improving the activity of Br . The computational results show that solvent polarity profoundly affects the activation barriers. To our delight, the activation barrier of the rate-determining step for the favored pathway in water is comparable (0.6 kcal/mol difference) with that in acetonitrile. The experimental observation further confirmed our results and demonstrated that the title reaction can be successfully achieved "on water." Therefore, we open a new efficient and green strategy for the synthesis of biphenol derivatives. © 2017 Wiley Periodicals, Inc.

Exploring the Effects of Water on the Mechanism of the Catalyst-Free Reaction between Isatin and 3-Methyl-2-pyrazolin-5-one from the Mixed Implicit/Explicit Multiple Types of Water Clusters

“…They concluded that while the implicit solvent effects of polar solvents do not substantially modify the gas-phase energies found along a pathway, the explicit inclusion of one solvent molecule favors the reaction to take place via a less-strained transition state. In light of the research work studied by Zheng and Zhang, − we find that the interaction between the water molecule cluster and reactants is very beneficial to the “on water” reaction; especially, it is the most favorable that the cluster models with two water molecules (called the two-water cluster) and the three water molecules (called the tri-water cluster) assist the intramolecular or intermolecular proton hydrogen transfer. Similarly, Jung and Marcus implemented the three-site water model to indicate that the hydrogen bond-mediated lowering of the energy barrier was the key origin for the enhanced acceleration of the cycloaddition reaction between quadricyclane and dimethyl azodicarboxylate .…”