▁of ▁ 2 , 4 - d init ro an il ine ▁( 5 ) ▁and ▁formation ▁of ▁the ▁König ▁salt ▁ ▁( 6 a ▁and ▁ 6 b ). ▁ ▁The ▁trans - cis - trans ▁is omer ▁of ▁the ▁König ▁salt ▁( 6 a ) ▁can ▁react ▁by ▁either ▁sig mat rop ic ▁re arr ang ement ▁or ▁nucle oph il ic ▁addition ▁of ▁a ▁zw itter ionic ▁intermediate ▁to ▁give ▁cycl ized ▁intermediate ▁( 7 ). ▁ ▁This ▁has ▁been ▁suggested ▁to ▁be ▁the ▁rate - det erm ining ▁step . ▁ ▁After ▁pro ton ▁transfer ▁and ▁am ine ▁elim ination , ▁the ▁desired ▁py rid in ium ▁ion ▁( 9 ) ▁is ▁formed . ▁ ▁This ▁mechanism ▁can ▁be ▁referred ▁to ▁as ▁an ▁instance ▁of ▁the ▁AN ROR C ▁mechanism : ▁nucle oph il ic ▁addition ▁( AN ), ▁ring ▁opening ▁and ▁ring ▁closing . ▁ ▁App lications ▁In ▁one ▁solid - phase ▁synth esis ▁application , ▁the ▁am ine ▁is ▁c oval ently ▁attached ▁to ▁Wang ▁res in . ▁ ▁Another ▁example ▁is ▁the ▁synth esis ▁of ▁a ▁ch iral ▁is o quin olin ium ▁salt . ▁ ▁Z in cke ▁al de hy des ▁ ▁With ▁secondary ▁am ines ▁and ▁not ▁primary ▁am ines ▁the ▁Z in cke ▁reaction ▁takes ▁on ▁a ▁different ▁shape ▁forming ▁so - called ▁Z in cke ▁al de hy des ▁in ▁which ▁the ▁py rid ine ▁ring ▁is ▁ring - open ed ▁with ▁the ▁terminal ▁im in ium ▁group ▁hydro ly zed