a Stock solutions of 1b and 2a were combined under air in a 4 mL vial equipped with a magnetic stir bar and septum. THF was added to adjust the final reaction concentration to 0.2 M. Commercial solutions of base were added to initiate the reaction, which was quenched after 10 min with 1 M HCl(aq), and a stock solution of 1,3,5-trimethoxybenzene was added as an internal standard. Reaction mixtures were evaporated and then analyzed by quantitative 1 H NMR spectroscopy.