Reaction of 2,3-diphenyl-5,6-dihydropyrazine and malononitrile to give 2,6-diamino-3,5-dicyano-4,10-diphenyl-1,7-diazatricyclo[5.2.1.04,10]deca-2,5-diene. A novel synthesis of a substituted diazadihydrotriquinacene