To vigorously stirred HMPA (15.0 g, 83.7 mmol) at 0 C°, a solution of triphosgene (11.28 g, 38.01 mmol) in dichloromethane (15 mL) was added over a period of 40 min. The ice bath was then removed and the mixture was stirred at room temperature. At various intervals, small aliquots were removed in order to follow the disappearance of the HMPA spectroscopically. After 3 h, the solvent was removed under reduced pressure to leave a residue. This residue was redissolved in dry dichloromethane (40 mL) and solid hydroxybenzotriazole monohydrate (12.76 g, 94.4 mmol) was added with stirring. The resulting solution was cooled to about 5 C° with an acetone/ice bath, whereupon triethylamine (8.42 g, 83.4 mmol) was added over a period of 15 min and stirring was continued at -5 C for 4 h. The residue was dissolved in water (50 mL) and mixed with a filtered solution of potassium hexafluorophosphate (16.68 g, 90.6 mmol) in water (120 mL) to give benzotriazolyl-N-oxytris(dimethylamino)phosphonium hexafluorophosphate 1317 (BOP) as a crystalline solid (28.91 g, 78%).
Chloroformates 1319 and chlorides 1320 are also formed when secondary benzyl alcohols 1318 are treated with trichloromethyl chloroformate (diphosgene) in the presence of triethylamine. The distribution of products can be controlled.
Reactions of tetrahydropyranylated alcohols 1321 with N,N-dimethylphosgeniminium chloride (‘‘Viehe salt’’) 1322 give the corresponding alkyl chloride 1300 in good yields [997]. This conversion can be conveniently accomplished by adding the ‘‘Viehe salt’’ (1.05 equiv.) as a solid to a solution of the THP-protected alcohol (1 equiv.) in anhydrous dichloromethane (0.3 m) under argon at 0 C°. After completion of the reaction and aqueous work-up, the crude alkyl chlorides are purified by column chromatography.
