Hantzsch reaction with <i>bis</i>-indole-2,3-diones: Synthesis of novel <i>bis</i>-spirocyclic oxindole incorporating acridine, dipyrazolo[3,4-<i>b</i>:4',3'-<i>e</i>]pyridine and pyrido[2,3-<i>d</i>:6,5-<i>d'</i>]dipyrimidine
Synthetic communications