General procedure for the synthesis of 7-bromo-2,2-dimethylchromen-4-one from m-bromophenol: About 15 g of polyphosphoric acid was added to a mixture of 3,3-dimethylacrylic acid (5.0 g, 54.9 mmol) and 3-bromophenol (10.4 g, 60.4 mmol). The mixture was stirred and reacted at 95 °C for 4 h under argon protection. Upon completion of the reaction, the reaction slurry was cooled to 0 °C with an ice bath, dissolved in 200 mL of ice water and subsequently extracted with ether (3 x 100 mL). The organic phase was separated and washed sequentially with 5N KOH aqueous solution (50 mL) and saturated saline (50 mL). The extract was dried over anhydrous magnesium sulfate, filtered and concentrated under reduced pressure. The crude product was purified by silica gel column chromatography (eluent: 5% ethyl acetate/hexane) to afford 7-bromo-2,2-dimethylchromen-4-one (2.80 g, 22% yield) as a brown solid.1H-NMR (300 MHz, CDCl3) data were as follows: δ 1.45 (s, 6H), 2.71 (s, 2H), 7.13 (m, 2H), and 7.72 (d, 1H, J = 8.3 Hz).
