Novel and potent Lewis acid catalyst: Br<sub>2</sub>-catalyzed Friedel–Crafts reactions of naphthols with aldehydes

<p>A discovery that the inexpensive Br<sub>2</sub> can serve as a potent Lewis acid catalyst for bis(2-hydroxy-1-naphthyl)methanes synthesis is presented. Under the catalysis of Br<sub>2</sub> at room temperature, naphthols reacted smoothly with various aldehydes with high efficiency and broad substrate scope. This reaction used to require highly acidic conditions and/or high temperature and/or pressure, and sometimes featured poor yields. Moreover, theoretical calculations suggested that Br<sub>2</sub> is a potent Lewis acid to activate the carbonyl group, yet it was not the primary cause for the remarkable activity of Br<sub>2</sub> in the current communication.</p>