NEW DEVELOPMENTS IN THE SYNTHESIS OF LOWER FLUORINATED PYRIDINES VIA DIAZOTIZATION-FLUORINATION OF AMINOPYRIDINES IN ANHYDROUS HYDROGEN FLUORIDE

Article abstract of DOI:10.1016/S0022-1139(00)82666-4

The isolation and stabilization of elusive 4-fluoropyridine as the hydrochloride salt (54percent yield) from fluorodediazoniation of 4-aminopyridine in anhydrous hydrogen fluoride (AHF) is described.Unlike the low yields (0-13percent) recently reported from the chlorodediazoniation of 2,6-diaminopyridine and 3-halo-2,6-diaminopyridine, fluorodediazoniation gave high yields (49-62percent) of the corresponding 2,6-difluoropyridines.In contrast, benzene analogs, i.e. m-phenylenediamine and 4-chloro-m-phenylenediamine, form only tars under similar fluorination conditions.Vicinal aminohalopyridines, e.g. 3-amino-2-chloropyridine and 2-amino-3,5-dichloropyridine give the corresponding fluorohalopyridine in 49-89percent yield.Again, the benzene analogs, i.e. o-chloroaniline and 2,4-dichloroaniline, resist fluorination.