An efficient transition-metal-free route to oligo-α-pyridylamines via fluoroarenes

The new polynucleating tripodal proligand H 6 tren(dpa) 3 , containing thirteen nitrogen donors of four different types, was designed, synthesized, and isolated in good yield (∼60%) via a transition-metal-free triple N-arylation of H 6 tren with HXdpa (X = Br or F), using K 2 CO 3 or Cs 2 CO 3 as a base (H 6 tren = tris(2-aminoethyl)amine, HXdpa = 6-halogeno-N-(pyridin-2-yl)pyridin-2-amine). HFdpa was prepared with excellent yield (90–92%) by reaction of 2,6-difluoropyridine with 2-aminopyridine in LiH/toluene/pyridine and was found more reactive than HBrdpa, affording higher conversion and higher yield. Use of Cs 2 CO 3 turned out to be essential for achieving high regioselectivity and eliminating overarylation almost completely.