Reaction #7299

Reaction equation

Methyl tert-butyl ether

Triethylamine

2-methyl-4-[pyridin-3-yl-(Z)-methylene]-4H-oxazol-5-one

methanol

Tetrafluoroboric acid

→

3-(2-Acetylamino-2-methoxycarbonylvinyl)pyridinium tetrafluoroborate

Conditions

Workup

1. 1
   Washwas rinsed with methanol (0.5 l) (the pH of a sample
2. 2
   Temperaturethe reaction solution was cooled to 30° C
3. 3
   workup.WAITWithin 1 h
4. 4
   Temperaturethe mixture was cooled to an internal temperature of 10° C. and (if required after seeding) the suspension
5. 5
   workup.STIRRINGthe mixture was stirred at 10° C. for 1 h
6. 6
   workup.ADDITIONThe suspension was introduced into a centrifuge which
7. 7
   Washcentrifuged, and the the product washed with methyl tert-butyl ether (20.0 l)
8. 8
   Otherdried at 40° C. under reduced pressure

Procedure

Under nitrogen, a suspension of 2-methyl-4-[pyridin-3-yl-(Z)-methylene]-4H-oxazol-5-one (12.0 kg, 63.83 mol) in methanol (120.0 l) was heated at 60° C. Triethylamine (0.5 l) was pumped in, and the apparatus was rinsed with methanol (0.5 l) (the pH of a sample taken, measured using a glass electrode, was pH 8.15). Within a period of 30 min, the reaction solution was cooled to 30° C. Tetrafluoroboric acid solution (48% strength in water, 11.8 kg, 64.5 mol) was added over a period of 30 min. Within 1 h, the mixture was cooled to an internal temperature of 10° C. and (if required after seeding) the suspension was then stirred at 10° C. for a further 3 h. Methyl tert-butyl ether (40.0 l) was added, and the mixture was stirred at 10° C. for 1 h. The suspension was introduced into a centrifuge which had been inertized with nitrogen, centrifuged, and the the product washed with methyl tert-butyl ether (20.0 l) and dried at 40° C. under reduced pressure. Yield: 18.7 kg (60.71 mol, 95.1% of theory). M.p.: 179.4° C.; MS (ESI+): m/z (%)=221 ([M+H+] of the free base, 100); 1H-NMR (200 MHz, DMSO-d6): δ=2.01 (s, 3H), 3.77 (s, 3H), 7.21 (s, 1H), 7.89 (dd, 1H), 8.48 (d, 1H), 8.76 (d, 1H), 8.98 (s, 1H), 9.92 (s, 1H); IR (KBr): ν=1726.9, 1670.1, 1091.5 cm−1.

Source