An efficient transition-metal-free route to oligo-$\alpha $-pyridylamines via fluoroarenes

Abstract

The new polynucleating tripodal proligand $\text{H}_6\text{tren(dpa)}_3$, containing thirteen nitrogen donors of four different types, was designed, synthesized, and isolated in good yield (${\sim }$60%) via a transition-metal-free triple N-arylation of $\text{H}_6$tren with HXdpa (X $=$ Br or F), using $\text{K}_2\text{CO}_3$ or $\text{Cs}_2\text{CO}_3$ as a base ($\text{H}_6$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 $\text{Cs}_2\text{CO}_3$ turned out to be essential for achieving high regioselectivity and eliminating overarylation almost completely.

Keywords

• Oligo-$\alpha $-pyridylamides
• Tripodal ligands
• Halopyridines
• Metal-free
• Buchwald–Hartwig
• EMACs