A tetrahydrofuran solution (60 mL) of magnesium scrapings (2.94 g, 2.00 eq.), a small amount of iodine and 1,2-dibromoethane was stirred at room temperature for 1 hour under argon protection. Subsequently, a tetrahydrofuran solution (20 mL) of 2-bromonaphthalene (25.00 g, 2.00 eq.) was slowly added dropwise at 27°C and the reaction mixture was warmed up to 40°C with continued stirring for 45 minutes. Next, the reaction system was cooled to -9°C, a tetrahydrofuran solution (10 mL) of diethyl phosphite (9.77 g, 0.06 mol) was added dropwise and the reaction was stirred at 2°C for 3 hours. Upon completion of the reaction, the temperature of the system was adjusted to -5°C and the reaction was quenched by the slow addition of water (20 mL), followed by the addition of toluene (60 mL) and 6 M hydrochloric acid (20 mL) for extraction. The organic layer was separated and washed sequentially with 5% aqueous sodium bicarbonate and 5% aqueous sodium chloride. The organic layer was dried over anhydrous magnesium sulfate, filtered and concentrated under reduced pressure. The resulting crude product was recrystallized with isopropyl ether/hexane mixed solvent and dried (under reduced pressure, 40°C) to give 1,1'-dinaphthylphosphine oxide (9.621 g, white powder) in 53.0% yield. The structure of the product was confirmed by 1H-NMR (300 MHz, CDCl3, TMS), 13C-NMR (75 MHz, CDCl3) and 31P-NMR (121 MHz, CDCl3, 85% H3PO4).
