Phosphate → (S)-7,8-dihydro-2,9-dimethoxy-7-methyl-6-phenanthridinol trifluoromethanesulfonate

Participants

Reaction Conditions

Reaction Steps

Trifluoromethanesulfonic anhydride (3.80 mL, 22.4 mmol, 1.10 equiv) was added via syringe to a suspension of (S)-7,8-dihydro-2,9-dimethoxy-7-methyl-6(5H)-phenanthridinone (10, 5.52 g, 20.3 mmol, 1 equiv) and 2,6-di-t-butylpyridine (6.10 mL, 27.1 mmol, 1.33 equiv) in dichloromethane (400 mL) at -78° C. The cold suspension was allowed to warm to 23° C. over 30 min and was stirred at that temperature for 15 min. Solids were observed to dissolve as the reaction proceeded. The reaction mixture was poured into aqueous phosphate buffer solution (pH 7, 0.05M in sodium hydrogen phosphate and 0.05M in potassium dihydrogen phosphate, 200 mL). The aqueous layer was separated and further extracted with two 200-mL portions of dichloromethane. The combined organic layers were dried over sodium sulfate and were concentrated in vacuo. The residue was purified by flash column chromatography (40% dichloromethane-hexanes) to provide (S)-7,8-dihydro-2,9-dimethoxy-7-methyl-6-phenanthridinol trifluoromethanesulfonate (ester) (12) as an off-white solid (mp 129.5°-130.5° C., 7.09 g, 86%).

Provenance & Evidence