1,3-Dipolar cycloaddition of cyanopyridines to heterocyclic N-imines – combined experimental and theoretical studies

Abstract

Series of 2-pyridyl substituted [1,2,4]triazolo[1,5-a]azines have been synthesized by reaction of cyanopyridines with N-aminoazinium mesitylenesulfonates under basic conditions. The reaction proceeds smoothly with pyridinium, 1,10-phenanthrolinium and 8-oxyquinolinium salts. In case of quinolinium and isoquinolinium salts dimers of corresponding N-imines were isolated. Pyrazinium- and pyridazinium-N-imines didn’t possess any reactivity toward cyanopyridines. DFT studies give high activation barriers for 4-cyanopyridine cycloaddition to quinolinium and pyrazinium-N-imnes as well as highly negative free energy of dimerisation for quinolinium and isoquinolinium-N-imnes.