1.2- Diaminobenzene reaction

Attempts to directly iodinate quinoxaline failed, and the synthesis of 2,3-diphenyl-5,8-dibromoquinoxaline is somewhat more involved (Scheme 9) [61]. Starting from ort/zo-phenylenediamine, reaction with SOCI2 gives benzothia-diazole in high yield. Bromination in HBr furnishes 4,7-dibromobenzothiadi-azole, which can be alkynylated or directly reduced [62]. Reduction of the dibromide with sodium borohydride leaves the halide substituents unmolested but opens the ring to furnish l,4-dibromo-2,3-diaminobenzene. Reaction of this intermediate with a 1,2-dione furnishes a 2,3-disubstituted 5,8-dibromo-quinoxaline. Pd-catalyzed alkynylation finishes the sequence off and removal of the TMS groups yields the desired 5,8-diethynylquinoxaline monomers (Table 9, entries 13,14). 

Reaction with an amino-propyl derivative of glass or hornblende with glutaraldehyde cross-linking reaction with titanium(iv) oxide coated with polymerized, diazotized 1,3-diaminobenzene Reaction with agarose activated with 4-benzoquinone Reaction with agarose cyclic imidocarbonate... 

Reaction with a copolymer of glutaraldehyde and diaminobenzene Reaction with beads of derivatized, macroreticular polystyrene 5.3.1.18 Reaction with a copolymer of... 

A general route to benzo-2,l,3-selenadiazoles involves the condensation reaction between 1,2-diaminobenzene and selenium tetrachloride. This method has also been used recently for the synthesis of 4,5,6,7-tetrafluoro-2,l,3-benzotelluradiazole (Eq. 2.9) ... 

The chemistry of 1,2,5-thiadiazole systems (RC)2N2S has been extensively investigated. " In addition to the condensation reactions of sulfur halides with 1,2-diaminobenzenes, this ring system is obtained in high yields by the reaction of S4N4 with acetylenes (Section 5.2.6). For example, the reaction of S4N4 with diphenylacetylene produces 3,4-diphenyl-1,2,5-thiadiazole in 87% yield. 

This section will focus primarily on a comparison of these ring systems with their heavier chalcogen analogues. The first selenium derivative benzo-l,2,5-selenadiazole was prepared more than 115 years ago by the condensation reaction of selenium dioxide with 1,2-diaminobenzene (Eq. 11.12) and other benzo derivatives may be prepared in a similar manner. The parent 1,2,5-selenadiazole has also been reported. This reagent has been employed to make the tellurium analogue via treatment with ethylmagnesium bromide followed by the addition of tellurium tetrachloride (Eq. 11.13). ... 

Aminoacroleins enter the transamination reaction with 1,2-diaminoethane to furnish bis adduct 217, whereas with 1,2-diaminobenzene they yield the 2 2 macrocyclic adduct 218 (77CZ161). 

Thus, ynaminoketones with 1,2-diaminobenzene form benzodiazepines with retention of the dialkylamino group. The reaction occurs as a nucleophilic addition in the absence of catalysts. With Q, /3-acetylenic ketones 1,2-diaminobenzene reacts in the same manner, but under proton-catalyzed conditions (72LA24). At the same time, ynamines and enynamines furnish with 1,2-diaminobenzene substituted benzimidazoles as aresultof double attack at the acetylene bond(83ZOR926 84ZOR1648). 

Diaminobiphenyl (former name benzidine) can be easily bisdiazotized, but is not cleanly monodiazotized by reaction with one equivalent of a nitrosating agent. However, 4-aminobiphenyl-4,-diazonium ions are formed in a triazene equilibration of a 1 1 mixture of 4,4 -diaminobiphenyl with biphenyl-4,4 -bisdiazonium salts in aqueous HC1 (Tauber, 1894 see also Sec. 13.4). Methods for mono- and bisdiazotiza-tion of 1,4-diaminobenzene (/ -phenylenediamine) have been described by Saunders and Allen (1985, p. 29 see also Sec. 2.2). 

If an aromatic o-diamine such as 1,2-diaminobenzene (2.24) is diazotized in dilute aqueous acid, the 2-aminobenzene-l-diazonium ion formed first (2.25) undergoes a rapid intramolecular N-azo coupling reaction to give 1,2,3-benzotri-azole (2.26). Both amino groups of 2.24 can, however, be diazotized in concentrated acid (Scheme 2-18), forming the bis-diazonium ion 2.27. 1,3- and 1,4-diamines must also be bisdiazotized in concentrated acids in order to avoid inter-molecular N- or C-coupling. 

The reaction also proceeds readily with A/-monosubstituted 1,2-diaminobenzenes (6.45, R = alkyl, aryl, acyl). Kroupa and Matrka (1970) investigated optimal reaction conditions for the synthesis of 1,2,3-benzotriazole from 1,2-diaminobenzene. 

By making the approximation that Ah = AG, we can calculate K for the ortho/para mixture of the diaminobenzenes starting from the ortho. At 300K, K = 5.8 X 10 3 and even at 250 C (523°K), K = 5.2 x 10 2. Thus we predict only 0.6% of the para isomer at room temperature and even at 250°C, a reasonable operating temperature, we predict only 5% of the para isomer. At this elevated temperature, of course, competing side reactions could occur destroying the diaminobenzenes. There is also a major separations problem to solve since the desired isomer must be extracted from the mixture. This is complicated by the fact that the desired para isomer would only be present at a few percent. 

Selenium(IV) reacts with substituted 1,2-diaminobenzene or 2,3-diamlnonaphthalene in acidic solution to form stable cyclic derivatives which can t>e extracted into an organic solvent and analyzed by gas or liquid chromatography [682,683]. With chloro-, bromo-, or nitro-substituents the plazselenols can be determined with an electron-capture detector at the low picogram level. Se(VI) does not form piazselenol derivatives so the reaction with diaminobenzene can be used to determine the concentration of Se(IV) and Se(VI). Selenium(VI) may be redu to Se(IV) with... 

An interesting example of an internal coupling reaction is provided by the diazotisation of o-diaminobenzene (36) ... 

A number of syntheses of heterocycles were performed using the MORE technique [17, 18]. While most of these reactions had been reported in Organic Synthesis to require reflux times of an hour or more, Bose et al. were able to obtain comparable yields in a matter of minutes. For example, benzimidazole 18 was synthesized from 1,2-diaminobenzene 17 and formic acid, which served as both reagent and solvent, in 70% yield in 3 min (Scheme 4.10), compared with the recommended heating time of 2 h [17]. 

The new method of Yoneda s group132 is also a one-pot diazotization-fluoro-de-diazoniation in a liquid-liquid two-phase mixture of pyridine and hydrogen fluoride. Yields for 25 aromatic amines and diamines are 50-100%, except for 2-and 3-fluorobenzoic acid, the three nitroanilines, 3- and 4-diaminobenzene and 4,4 -diaminodiphenyl-oxide (10-50%). In their 1994 paper the authors demonstrate that, in the same system, the photochemical decomposition gives in many cases significantly higher yields than the thermal reaction. The most spectacular increase in yield was found for the fluorination of 2-fluoroaniline where o-difluorobenzene was obtained photochemically in 80.2% yield, but thermally only in 0.6% ... 

In the conversion of 3,4,5,6-tetrabromo-l,2-bis(bromomethyl)benzene into the tetrabromoisoindole (Scheme 5.4), the bisalkylation of the primary amine in the First step of the reaction is promoted by the addition of benzyltrimethylammonium methoxide [22]. 2-Chloromethylpyridine reacts with a series of a,co-diaminoalkanes, as well as 1,2-diaminobenzene, to produce Af V -dialkylated and N,N,N N -tctra-alkylated products [23]. 

The analogous reaction of benzyl and butyl naphthylcarbamates and of benzyl phenylcarbamates has been carried out in good yield under both liquiddiquid and solidrliquid two-phase conditions, using benzyltriethylammonium chloride as the catalyst [16, 17]. A similarly catalysed /V-alkylation of the ethyl carbamic esters derived from 1,2-diaminobenzene is reported [17] to lead to the formation of 1,3-dialkylbenzimidazol-3-ones (Scheme 5.7). 

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