1.2- Diarylamines, formation

The addition of 2,2, 4,4, 6-pentanitro-6 -methyldiphenylamine [64653-47-0] to seawater precipitates potassium (38). Aromatic amines, especially aminotetrahydronaphthalenes and their A[-aryl derivatives, are efficient flotation agents for quartz. The use of DPA for image formation in films has been patented (39,40). Diarylamines are used as intermediates (41) for azo, sulfur, oxidative base, triaryhnethane, oxazine, nitro, and safranine dyes (see Dyes and DYE INTERLffiDIATES). 

Brick et al. have studied this bromination in more detail and showed that the extent of the bromination can be controlled by changing the ratio of the reagents. The first substitution was found to be in the para position but subsequent intramolecular rearrangements allowed the formation of 2-5-dibrominated species. Brick et al. also reported the functionalization of such species using Pd-catalyzed reactions such as Heck and Suzuki couplings to give fully substituted p-stilbenes, p-biphenyls, diarylamines, and methylcinnamates. Hydrogenation of... 

Indeed, palladium complexes ligated by P(/-Bu)3 catalyzed the formation of aryl piperazines from aryl halides and piperazine in high yields with turnover numbers of 7,000 at 120 °C.56 These complexes also catalyzed the formation of triarylamines from aryl halides and diarylamines with turnovers of 4,000. 

In addition, complexes of P(/-Bu)3 have been shown to catalyze the formation of diaryl heteroarylamines from bromothiophenes.224 Aminations of five-membered heterocyclic halides such as furans and thiophenes are limited because their electron-rich character makes oxidative addition of the heteroaryl halide and reductive elimination of amine slower than it is for simple aryl halides. Reactions of diarylamines with 3-bromothiophenes occurred in higher yields than did reactions of 2-bromothiophene, but reactions of substituted bromothiophenes occurred in more variable yields. The yields for reactions of these substrates in the presence of catalysts bearing P(/-Bu)3 as ligand were much higher than those in the presence of catalysts ligated by arylphosphines. 

Nitrenium ions can be viewed as products from two-electron oxidation of amines (Fig. 13.13) followed by loss of a proton. Thus they need to be considered as intermediates in the oxidation of amines. In two early studies, diarylnitrenium ions were shown to have formed in the oxidation of diarylamines. Svanholm and Parker carried out cyclic voltammetry on A,A-di-(2,4-methoxyphenyl)amine (25) in acetonitrile with alumina added to suppress any adventitious nucleophiles. The voltam-mogram revealed two sequential oxidation processes (1) formation of the cation radical 26, and (2) either the nitrenium ion 27 or its conjugate acid. In strongly acidic solution the latter was sufficiently stable that its absorption spectrum could be recorded. 

Diarylamines will also usually require strong acylating agents to undergo acylation. If Lewis acids such as ZnCl2 are used as catalysts the formation of an acridine can compete with N-acylation (Bemthsen acridine synthesis last reaction, Scheme 7.10). 

All these reactions proceed by initial base-promoted formation of copper amide complexes 306A from diarylamines or sulfonamides 306 or 308, respectively, which are subject to a concerted, sv -amidocupration with the adjacent alkene unit via transition state 306B (Fig. 82). The resulting alkylcopper(II) intermediates 306C are... 

The palladium-catalyzed formation of diarylamines has been used in several contexts to form molecules with biological relevance. The ability to prepare haloarenes selectively by an ortho-metallation halogenation sequence allows for the selective delivery of an amino group to a substituted aromatic structure. Snieckus has used directed metallation to form aryl halides that were subsequently reacted with anilines to prepare diarylamines (Eq. 34)) [156]. Frost and Mendon a have reported an iterative strategy to prepare (by palladium-catalyzed chemistry) amides and sulfonamides that may act as peptidomimetics. Diarylamine units are constructed using the DPPF-ligated palladium catalysts, and the products are then acylated or sulfo-nated with 4-bromo benzoyl or arylsulfonyl chlorides [157]. 

Several recent papers have reported the palladium-catalyzed formation of diarylamines to prepare nucleosides of damaged DNA. Sigurdsson, Hopkins et al. reported the formation of... 

Photocyclization of A -methyl-(p-methoxyphenyl)anilines in the presence of aqueous hydrochloric acid gave a set of carbazolones, as illustrated by the conversion of the diarylamine 241 into the system 242 (Equation 77) <2002CC270>. In addition, it has been reported previously that photocyclization of fluorine-substituted diphenyl-amines leads to formation of carbazoles <1996J(P1)669>. 

Nishiyama, and co-workers first reported that the catalyst derived from Pd(OAc)2 and (f-Bu)3P effects the C-N bond formation to produce triarylamines in excellent yield [65]. This system also is useful in the coupling of diarylamines and aryl chlorides. Hartwig and co-workers found this protocol optimal for the preparation of triarylamines. The (f-Bu)3P/Pd-catalyst was sufficiently active such that the coupfing of diarylamines and aryl bromides can be performed at room temperature,Eq. (34) [50]. The (f-Bu)3P/Pd-system has been used to produce new triarylamine-based polymers [ 64 a - d]. 

Grellmann and co-workers, who have contributed considerably to this area with their work on the photocyclization of diarylamines to carbazoles, now report that the only unknown isomer (157) of the five possible indolocar-bazoles can be conveniently synthesized from (158) in methylcyclohexane solution by using 300 nm radiation.Flash experiments and steady-state studies show that the formation of (157) occurs adiabatically in the triplet manifold by a two-photon process and a triplet energy transfer reaction prevents accumulation of large concentrations of the intermediate photoproduct (159). Photocyclization of the aryl-ethenyl compounds (160) has been... 

Direct amidation can be carried out if an aromatic compound is heated with a hydroxamic acid (34) in polyphosphoric acid, but the scope is essentially limited to phenolic ethers.The reaction of an aromatic compound with aniline, BU4NF and KMn04 led to the diarylamine. The formation of hydroindole derivatives was accomplished by reaction of a A-carbamoyl phenylethylamine derivative with phenyliodine (III) diacetate, followed by Bu4NF. Direct amidation via ipso substitution by nitrogen was accomplished when a A -methoxy arylethylamide (35) was... 

For the reactions of aryl halides with diarylamines (equation 17), the P(tol-o)3 ligand gives good yields in most cases, but catalyst loads of 5-10% were typically required99. In some cases, palladium complexes bearing DPPF as ligand are more effective catalysts for the formation of triarylamines, and can even produce unsymmetrical triarylamines in a one-step addition of two aryl halides sequentially to an aniline100. 

Thus, it was shown that the tautomerization may be of importance in the thermal dehalogenation of chloroaromatics14. The formation of diarylamines in this reaction can be also explained by the presence of aniline tautomers in the reaction mixtures14. One of the well-known types of aniline tautomerism is the enol-imine-keto-amine equilibrium. In effect, it is a reversible conversion of Schiff bases into enamines that is frequently employed for the synthesis of photochromic compounds, as well as of mesomorphic... 

In the Ullmann synthesis, the presence of an amino group results in the formation of a diarylamine ... 

One of the most versatile approaches to highly functionalized carbazoles is the sequential palladium-catalyzed C-N/C-C coupling for assembly of the central pyrrole moiety. Many total syntheses of naturally occurring carbazole alkaloids are following this route. The initial C-N bond formation by a palladium(0)-cata-lyzed Buchwald-Hartwig amination of aryl halides or triflates 94 with arylamines 31 affords the diarylamines 95 (Scheme 24) [139,140]. Oxidative cyclization of the diarylamines 95 to the carbazoles 32 proceeds via a double C-H bond activation and is achieved in the presence of palladium(ll) compounds. 

It is well known that, depending on the structure of the hydrazo com-poiuid, there is not only rearrangement into 4,4 -positions (formation of benzidine), but also formation of the respective diaryl-2,4 - and 2,2 -diamines (e.g. diphenyline- and o-benzidine-reari angements) and of 2- and 4-amino-diarylamines (semidines). In certain cases even formation of carbazoles accompanied by release of ammonia has been observed. 

The reactions of diarylamines with aryl halides is more straightforward than the reaction of secondary alkylamines because these substrates possess no hydrogens on the a carbon and cannot, therefore, nndergo /3-hydrogen elimination as palladium amides. However, competitive formation of arene by an nnknown mechanism remains one side prodnct. For the most part, the synthesis of triarylamines has focused on the preparation of discrete molecules and polymers that are important for electronic materials applications,... 

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