Condensation of o-phenylenediamine with suitable $-dicarbonyl compounds gives rise to 1,5_benzodiazepines substituted in the 3-position. Thus the synthesis of 2,3,4-trimethyl-1,5_benzodiazepine (1) I,2 3 ' has been described. However, all attempts to obtain o-phenylenediamine From this reaction unknown structure. yellow base in low the corresponding 2,3,3,4_tetramethylbenzodiazepine (2) from 5 and 3,3-dimethylpentan-2,4-dione have proved unsuccessful. Vaismanl isolated a yellow base in 1940 (Vaisman's base) of Subsequently Halford and Fitch' confirmed formation of the yield. These authors suggested that formation of (2) would involve penetration of one of the methyl groups into the benzene II-orbital region leading to a highly-strained ring. They showed further that the base had a likely composition of C 17H20N4 with an equivalent weight of about 274. No final structure was proposed, however. While pursuing our synthesis of macrocycles', and in particular those macrocycles bearing N atoms in the ring, we obtained a yellow base apparently identical to Vaisman's product for which we now propose the phenazine structure (3) ?"z (j)R=H (3) (Z)R=W Refluxing equimolar proportions of o-phenylenediamine