 Upon heating a primary amine with the "N"-2,4-dinitrophenyl-pyridinium salt (2), the addition of the amine leads to the opening of the pyridinium ring.A second addition of amine leads to the displacement of 2,4-dinitroaniline (5) and formation of the König salt  (6a and 6b).The trans-cis-trans isomer of the König salt (6a) can react by either sigmatropic rearrangement or nucleophilic addition of a zwitterionic intermediate to give cyclized intermediate (7).