To obtain the subject compound useful as a fluorine atom introducing agent by reacting a pyridine compound with boron trifluoride and a fluorine gas in the presence of both water and hydrogen fluoride.
A pyridine compound of formula I (R1 to R4 are each H, a halogen, an alkyl, an aryl, an acyl, an alkoxycarbonyl, an aryloxycarbonyl, nitro, cyano, hydroxy, amino, etc.) is reacted with boron trifluoride and a fluorine gas in an organic solvent (e.g. acetonitrile) in the presence water and hydrogen fluoride at -100 to 40°C for 3-5 hours to give an N- fluorohyridiniumtetrafluoroborate of formula II. The amount of water is 1-150mol% based on the compound of formula I, that of hydrogen fluoride is 1-150mol% and that of boron trifluoride is 1-1.2 equivalent. The presence of water is essentially required for this reaction but the objective substance is undesirably hydrolyzed by the excessive existence of water.
NUKUI KAZUNORI
KAWADA TSUNESUKE
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