Reaction Steps
A round bottom flask was charged with 1-(2-(1H-pyrrol-1-yl)phenyl)-2,2,6,6-tetramethylphosphinan-4-one (878 mg, 2.80 mmol, 1.0 equiv) and purged with nitrogen for 15 minutes. Then nitrogen-sparged diethylene glycol (14.7 mL, 154 mmol, 55 equiv) was added and the flask was equipped with a Claisen adapter and a Dean-Stark trap. The flask was further charged with hydrazine hydrate (1.24 mL, 14.0 mmol, 5 equiv, 55 wt % hydrazine) and potassium hydroxide (786 mg, 14.0 mmol, 5 equiv), and the mixture was immersed in an oil bath at 60° C. The temperature of the bath was gradually increased to 210° C. over 1 hour and kept at that temperature for 7 hours. The reaction mixture was cooled to room temperature under a positive pressure of nitrogen and then diluted with water (50 mL) and ethyl acetate (20 mL). The phases were partitioned, and the organic layer was collected. The aqueous layer was washed with ethyl acetate (4×20 mL), and the combined organic fractions were washed once with aqueous saturated sodium chloride, dried over sodium sulfate, filtered, and concentrated on a rotary evaporator to afford the title compound as a pale yellow solid (811 mg, 91 area % by HPLC, 97% yield). 1H NMR (400 MHz, CDCl3) δ ppm 7.96-7.83 (m, 1H), 7.35-7.22 (m, 2H), 7.22-7.17 (m, 1H), 6.72-6.66 (m, 2H), 6.20 (t, J=2.1 Hz, 2H), 1.87-1.71 (m, 2H), 1.71-1.56 (m, 2H), 1.50-1.33 (m, 2H), 1.11 (s, 3H), 1.06 (s, 3H), 0.76 (d, J=9.7 Hz, 6H). 13C NMR (100 MHz, CDCl3) δ ppm 149.4-146.8 (m), 134.7 (d, J=4 Hz), 129.0, 127.8 (d, J=3 Hz), 126.5, 123.3 (d, J=3 Hz), 107.9, 37.6, 31.4, 31.1, 30.2 (d, J=7 Hz), 29.6 (d, J=18 Hz), 20.5. 31P NMR (CDCl3, 202 MHz) δ ppm −7.6 (s).
