Electrophilic fluorination with N,N′-difluoro-2,2′-bipyridinium salt and elemental fluorine

N,N'-Difluoro-2,2'-bipyridinium bis(tetrafluoroborate) (NEC-31) was shown to be a highly reactive electrophilic fluorinating agent with the highest effective fluorine content in its class. We have developed the perfect recycled fluorination system with NEC-31 for the lower-cost industrial fluorination and for an environment. MEC-31 can be completely recycled including the counter-anion. We found the fluorination of 2-naphthol in liquid CO2 with MEC-31 in the presence of catalytic amount of NaOTf proceeded quantitatively without the generation of by-product. In the fluorination of 1,3-dicarbonyl compounds with elemental fluorine, we found the introduction method of fluorine gas would be very important in order to make a reaction efficient. As fluorination goes on, the quantity of 1,3-dicarbonyl compounds of the starting material is reduced gradually, and therefore the quantity of fluorine must be reduced by the method to control the flow rate or the concentration of fluorine gas diluted with nitrogen, together the fluorination to proceed efficiently. (C) 2002 Elsevier Science B.V. All rights reserved.