The preparation of phenazines by the cyclisation of 2-nitrodiphenylamines

Protonated nitro group as a gas-phase electrophile: Experimental and theoretical study of the cyclization of o-nitrodiphenyl ethers, amines, and sulfides

“…Sulfides 5 to 8 were synthesized from appropriate sodium thiophenoxide and chloronitrobenzene as reported previously [27] and purified by recrystallisation from ethanol. Amines 10 to 12 were synthesized from appropriate chloronitrobenzene and toluidine, as previously reported [5,28]. The amines were purified by column chromatography on silica gel by using a 1:9 mixture of chloroform and hexane as eluent.…”

“…12 , from M 5 requires less energy than passing over the previous transition state, TS 4 ; hence there would be sufficient available energy to drive the first loss of OH radical (Tables 4a, 4b, Scheme 3). In addition, we performed CASSCF type calculations on M 5 and transition states for OH radical loss from even-electron M 5 : TS(M 5 -P 12 ) and TS(M 5 -P 13 ) yielding P 12 and P 13 , respectively (Table 4c). The results indicate, although direct comparison is not possible, that the reverse activation energy for the loss process is small for amine 9 and sulfide 5 and moderate for ether 1 cases.…”

“…This could occur if the nitro group becomes an electrophile upon protonation. The only example, to our knowledge, is the cyclization of 4′-chloro-2-nitro-N-phenyl aniline in concentrated sulfuric acid to yield 2-chloro phenazine at 180 °C and 2-chloro phenazine-10-oxide at low temperatures [5].…”

Synthesis of phenazines by Cu-catalyzed homocoupling of 2-halogen anilines in water

“…Among the catalysts investigated, complex 1 exhibited preferable catalytic activity in 53% yield ( 4 NBr to be the best one in 79% yield (Table 1, entries 15,16). Furthermore, the catalyst, base and PTC loading was then investigated, and it was observed that decreasing the amount of the catalyst, base or PTC resulted in lower yields (Table 1, entries 17e20).…”

Synthesis and Crystal Structure of a Phenazine N-oxide

“…This condensation is an intramolecular variant of the Wohl-Aue reaction in which an aromatic nitro compound is condensed with an aniline in the presence of base to furnish a phenazine [1]. Investigations of the mechanism of the Wohl-Aue reaction have shown that the N-oxide, which is present in compound 1 , is an intermediate in the formation of phenazines which may become the main product depending on the reaction conditions [2]. Since formation of the phenazine from the N-oxide in basic media may be a thermal deoxygenation process, the title compound 1 likely was isolated due to the mild conditions applied in our synthetic procedure.…”