Triethyloxonium tetrafluoroborate → HCID 12834621, compound

3.8 g. (20 mmol.) of 7-phenyl-1,2,3,4-tetrahydro-1,4-diazepine-5-one (Compound XXV) were suspended in 100 ml. of dry methylene chloride stirred under nitrogen at room temperature. 4.0 g. (21 mmol.) of triethyloxonium tetrafluoroborate were added portionwise to the stirred suspension so as to maintain the reaction mixture at a temperature of 20°-25° C., the reaction being slightly exothermic. After the addition was completed, the reaction mixture was stirred for an additional 30 minutes at room temperature. The reaction mixture was then washed with cold dilute sodium hydroxide solution and dried over anhydrous sodium sulfate. The methylene chloride was evaporated off at reduced pressure and ether was added to the residue. A small amount of solid that did not dissolve was removed by filtration, and the filtrate was evaporated at reduced pressure to yield an oil which crystallized overnight in a refrigerator yielding the crude product (3.5 g.), m.p. 89°-93.5° C. Recrystallization from ether/heptane yielded the pure product as white crystals (1.6 g.), m.p. 94°-95.5° C. A second crop (1.6 g.) was obtained from the mother liquor, m.p. 89°-93° C.