An Efficient Transition-metal-free Route to Oligo-α-pyridylamines via Fluoroarenes

The new polynucleating tripodal proligand H6tren(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 H6tren with HXdpa (X = Br or F), using K2CO3 or Cs2CO3 as a base (H6tren = 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/py and was found more reactive than HBrdpa, affording higher conversion and higher yield. Use of Cs2CO3 turned out to be essential for achieving high regioselectivity and eliminating overarylation almost completely.