Vanadium-Catalyzed Selective Oxidative Homocoupling of Alkenyl Phenols To Synthesize Lignan Analogs

The oxidative homocoupling of para-alkenyl phenols and subsequent trapping of the resulting quinone methide with a variety of oxygen and nitrogen nucleophiles were achieved. Both beta-beta and beta-O coupling isomers can be synthesized via either C-C coupling and two nucleophilic additions of one water molecule (beta-beta isomer) or C-O coupling followed by one nucleophilic addition of a water molecule (beta-O isomer), respectively. Selectivity between these outcomes was achieved by leveraging the understanding of the mechanism. Specifically, a qualitative predictive model for the selectivity of the coupling was formulated based on catalyst electronics, solvent polarity, and concentration.