Abstract1,4‐Diphenylphthalazine (1) was reduced in tetrahydrofuran by sodium metal to a monomeric dianion2. Chemical reactions of this new dianion were examined with various reagents. Generally, the protonation, acylation and alkylation products were 1,2‐dihydrophthalazine derivatives. An annulation of the phthalazine ring system was accomplished by treating the dianion with 1,3‐dichloropropane or 1,4‐dichlorobutane. With 1,2‐dichloroethane however, only 1,4‐diphenylnaphthalene w