Pseudo Vilsmeier reagents a new protocol for regiospecific C-C bond formation in pyridines

Article abstract of DOI:10.1016/S0040-4039(99)01340-4

2-Fluoro- and 2,6-difluoropyridine are readily quaternised with methyl p-toluenesulfonate and methyl triflate respectively. These salts readily undergo substitution of fluorine by enamines, the difluoro-derivatives being capable of specific mono- or disubstitution in a symmetrical or unsymmetrical manner. The products reduced to give keto-1, 2, 3, 6-tetrahydropyridines, can be hydrosed to the corresponding ketopyridines or hydrogenated to give ketopiperidines.