Figure 2: Synthesis of diazatetracene 11b and diazapentacenes 15.

(a) The condensation of the diamine 9 with the ortho-quinones 10a and 10b furnished the diazaacenes 11a and 11b in excellent yield. (b) On reacting 13 with 10, the NH intermediates 14a–c are isolated and oxidized efficiently to 15a–c, respectively, by manganese dioxide.