Trimethyl borate → 2-(4-Amino-1,2,5-oxadiazol-3-yl)-4-chloro-1-ethyl-1H-imidazo[4,5-c]pyridin-7-ol

Participants

Reaction Conditions

Reaction Steps

A suspension of 4-(7-bromo-4-chloro-1-ethyl-1H-imidazo[4,5-c]pyridin-2-yl)-1,2,5-oxadiazol-3-amine (VI, 50 g, 0.14 mol) in THF (1 L) was cooled in a dry-ice/acetone bath until the internal temperature was below −75° C. Isopropyl magnesium chloride (225 mL, 2M in ether, 0.45 mol) was added slowly at a rate to keep the reaction temperature below −70° C. After an additional 10 min., trimethyl borate (54 mL, 0.48 mol) was added and the reaction was maintained in the dry-ice acetone bath for 1 h. The bath was removed and the reaction was allowed to reach ambient temperature. After 18 h., the resultant yellow suspension was cooled to 0° C. A solution of 30% hydrogen peroxide (250 mL) and 3N NaOH (100 mL) was added at a rate to keep the reaction temperature below 40° C. The ice bath was then removed and the reaction was stirred vigorously at ambient temperature for 2 h. The bulk of the organic solvent was removed under reduced pressure and the aqueous layer was acidified to pH 3 with 1N HCl. After stirring the resulting suspension for 30 min., ethyl acetate (200 mL) was added. After stirring for another 1 h, the solid was collected by filtration. The filter cake was washed sequentially with water, ethyl acetate, toluene and ethyl acetate. The solid was dried to a constant weight to give 35.9 g (88% yield) of the desired compound (VII) as a pale yellow solid. This was used without further purification. MS (ES+) m/z 281.3 (M+H)+.

Provenance & Evidence