Ethyl Methanesulfonate → Ethyl (diethoxyphosphoryl)methanesulfonate

A solution of ethyl methanesulfonate (4.14 mL, 40.2 mmol) in anhydrous tetrahydrofuran (100 ml) was cooled to −78° C. under a nitrogen atmosphere. N-Butyllithium (20 ml, 50.0 mmol) was added slowly in 7 minutes after which stirring was continued for 15 minutes. Diethyl phosphorochloridate (4.36 mL, 30.2 mmol) was added, the reaction mixture was stirred for 2.5 h, the cooling bath was removed and the mixture was allowed to reach room temperature. The reaction mixture was quenched with aqueous saturated ammonium chloride (150 ml) and the resulting mixture was extracted with EtOAc (2×100 ml). The combined extracts were dried over sodium sulfate and concentrated under reduced pressure to yield 9.20 g of a yellow oil. The oil was purified over silicagel (600 g) using a gradient of ethyl acetate (0-100%) in heptane to yield 1.75 g of the product (6.7 mol, 17%).