Synthesis
Method 2: Di-tert-butyl phosphate [20 g, 94 mmol (obtained from di-tert-butyl phosphite by the method of Zwierzak and Kluba, Tetrahedron, Vol. 27,3163 (1971)] was dissolved in methanol, and tetrabutylammonium hydroxide (47 mL 1M solution, 47 mmol) was added. The temperature of the reaction mixture was 23 °C and the initial pH was 4.33. The pH of the reaction mixture was adjusted to 6.5-7.0 by dropwise addition of methanolic tetrabutylammonium hydroxide (48 mL 1M solution, 48 mmol) within 0.2 h. The reaction mixture was stirred at about 2 °C for 0.5 h, followed by concentration under reduced pressure at bath temperatures lower than 40 °C. The reaction was carried out at a temperature of 0.5 °C for 0.5 h. The reaction was then concentrated by addition of tetrabutylammonium hydroxide to methanol. The crude product was dehydrated by azeotropic addition of toluene (3 x 100 mL) and concentrated again under reduced pressure. The crude residue was ground in cold hexane (0 °C) for 1 h. The solid was collected by filtration, washed with a minimal amount of cold hexane and dried to give the first batch of tetrabutyl di-tert-butyl ammonium phosphate (24.0 g) as a white solid. The mother liquor was concentrated under reduced pressure and then ground in cold hexane (20 mL) for 1 h. The solid was collected by filtration, washed with a minimal amount of cold hexane and dried to give the second batch of tetrabutyl di-tert-butyl ammonium phosphate (8.5 g) in a total yield of 32.5 g (77%). A solution of tetrabutylammonium di-tert-butyl phosphate (218 g, 480 mmol) in benzene (200 mL) was added dropwise to stirred chloroiodomethane (800 g, 4535 mmol) over a period of 1.5 hours at room temperature. The reaction mixture was continued to be stirred at room temperature for 1.5 hours and subsequently concentrated under reduced pressure. The oily residue was dissolved in Et2O and filtered to remove the precipitated white solid. The organic layer was washed sequentially with saturated NaHCO3 and H2O/brine (1/1), then dried with magnesium sulfate, filtered and concentrated under reduced pressure to give a reddish-brown oily substance (320 g). The oily substance was purified by column chromatography on silica gel (800 g), eluting sequentially with 20% EtOAc/hexane, 25% EtOAc/hexane, and 30% EtOAc/hexane. The product-containing fractions were collected and concentrated under reduced pressure to give a golden yellow oily substance. The oily substance was diluted with CH2Cl2 (30 mL), concentrated under reduced pressure and dried under vacuum to give the target compound 3 (61.3 g, 49% yield).1H NMR (benzene-d6) δ 5.20 (2H, d, J=15Hz), 1.22 (18H, s).
