Hydrochloric Acid → Di-tert-butyl (chloromethyl) phosphate

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Di-tert-butyl phospohite (40.36 mmole) was combined with potassium bicarbonate (24.22 mmole) in 35 ml of water. The solution was stirred in an ice bath and potassium permanganate (28.25 mmole) was added in three equal portions over one hour's time, The reaction as then allowed to continue at room temperature for an additional half hour, Decolorizing carbon (600 mg) was then incorporated as the reaction was heated to 60° C. for 15 minutes. The reaction was then vacuum filtered to remove solid magnesium dioxide. The solid was washed several times with water. The filtrate was then combined with one gram of decolorizing carbon and heated at 60° C. for an additional twenty minutes. The solution was again filtered to yield a colorless solution, which was then evaporated under vacuum to afford crude Di-tert-butyl phosphate potassium salt. Di-tert-butyl phosphate potassium salt (5 g, 20.14 mmole) was dissolved in methanol (15 g): to this solution at 0° C., a slight excess of concentrated HCl is slowly added with efficient stirring at 0° C. The addition of acid causes the precipitation of potassium chloride. The solid is then filtered and washed with methanol. The compound in the mother liquor is then converted to the ammonium form by adding an equal molar amount of tetramethylammonium hydroxide (3.65 g, 20.14 mmole) while keeping the reaction cooled by a salt/ice bath with efficient stirring. The resulting clear solution is placed under reduced pressure to give the elude product. To the tetramethylammonium di-tert-butyl-phosphate dissolved in refluxing dimethoxyethane is then added 4.3 grams of chloroiodomethane (24.16 mmole) and stirred for 1-2 hours. The reaction is then filtered and the filtrate is placed under reduced pressure to concentrate the solution in DME. The chloromethyl di-tert-butyl phosphate 12-16% in DME is used in the synthesis of 4-(5-(2-(3,5-bis(trifluoromethyl)phenyl)-N,2-dimethylpropanamido)-4-(o-tolyl)pyridin-2-yl)-1-methyl-1-((phosphonooxy)methyl)piperazin-1-ium without further purifications (60% yield): 1HNMR (CD3OD, 300 MHz) δ 1.51 (s, 12H, 5.63 (d, 2H, J=14.8). 31P-NMR (CD3OD, 300 MHz) δ −11.3 (s, 1 P).

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