Mechanistic investigation inspired "on water" reaction for hydrobromic acid-catalyzed Friedel-Crafts-type reaction of β-naphthol and formaldehyde.

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-H2 O co-catalyzed the preferential pathway undergoes the concerted nucleophilic addition and hydrogen shift, stepwise followed by H2 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.