Antitumour polycyclic acridines. Part 9.1 Synthesis of 7H-pyrido[4,3,2-kl]acridines with basic side chains

[3 + 2] Cycloaddition of 3-(dialkylamino)-1-triphenylphosphoranylidenepropan-2-ones and 9-azidoacridine affords 9-[5-(dialkylaminomethyl)-1H-1,2,3-triazol-1-yl]acridines. Graebe–Ullmann thermolysis of the triazoles has been guided by differential scanning calorimetry to predict the optimum temperature for nitrogen extrusion. Boiling diphenyl ether (bp 259 °C) is a suitable solvent to convert the triazolylacridines to 2-(dialkylaminomethyl)-7H-pyrido[4,3,2-kl]acridines.