Substituted diarylamines

Given the improved thermal stability of diarylamine substituted chromophores, we have developed a number of routes to materials of this type. For tethered substituents, the chromophores may be attached to the oxygen of 3,5-daminophenol by either SN-2... 

Nitroxyl radicals of diarylamines can also be obtained on oxidation with hydrogen peroxide in the presence of vanadium ions. Resonance helps stabili2e these radicals. Eor example, the nitroxide from 4,4 -dimethoxydiphenylainine [63619-50-1] is stable for years, whereas the radical from the unsubstituted diphenylamine caimot be isolated. Substitution in the ortho and para positions also increases the stabiUties of these nitroxides by inhibiting coupling reactions at these sites. However, they are not as stable as the stericaHy hindered tetramethylpiperidyl radical. 

Electrophilic substitution reactions of diarylamines are easily accompHshed since the amino group activates the aromatic ring. Thus, DPA reacts with bromine or chlorine to form the 2,2H,4 tetrahalo derivative nitration usually produces the trinitro compound. 

Good yields of 10-aryl-3,6-dinitroacridones were obtained merely by heating 2,2, 4,4 -tetranitrobenzophenone (419) with an excess of the corresponding aryl amines at 125°C. For example, aniline provided 420 in 80% yield (Eq. 38). The reaction is fairly general for meta- and para-substituted anilines, though it proceeds less readily with orf/io-substituted compounds (79JCS(P1)1364). A method of isolation of the intermediate diarylamine in the synthesis of certain 10-aryl-3,6-dinitroacridones from 2,2, 4,4 -tetranitrobenzophenone has also been described (93JCR(M)2779). 

Diarylamines couple with considerably more difficulty than alkylarylamines. In contrast to primary aromatic amines and alkylarylamines, dialkylarylamines are substituted by diazonium ions only in the 4-, not in the 2-position. This is due to the considerable sensitivity of azo coupling reactions to steric hindrance. 

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... 

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. 

The oxidative cyclization of Ar,Ar-diarylamines to carbazoles has been achieved by thermal or photolytic induction [7, 75]. However, the yields for this transformation are mostly moderate. Better results are obtained by the palladium(II)-mediated oxidative cyclization of Ar,Ar-diarylamines (Scheme 27). Oxidative cyclization by heating of the Ar,Ar-diarylamines 76 in the presence of a stoichiometric amount of palladium(II) acetate in acetic acid under reflux provides the corresponding 3-substituted carbazoles 77 in 70-80% yield [118]. The cou-... 

The first synthesis of an optically active isopavine, (—)-reframoline (29), has been achieved by the acid-catalyzed double cyclization process described previously. The properly substituted diarylamine 109 was resolved using (-t-)-di-benzoyltartaric acid to afford the (-I-) enantiomer. Conversion to the acetal 110 was accomplished without racemization. Subsequent acid-catalyzed cyclization yielded the levorotatory alkaloid 29 (Scheme 21) 112). 

There has been a review of die effects of high pressure on the substitution reactions of amines witii haloaromatic compounds, including polyhalobenzenes.17 Nucleophilic substiditions by amines often proceed readily hi dimethyl sulfoxide (DMSO). The pKa values, hi DMSO, have been reported for some ammonium ions derived from amines widely used as nucleophiles in 5nAt reactions.18 Correlations have been established19 between die oxidation potentials and the basicities of some arylamhie and diarylamine anions and die rate constants for dieir reactions with aiyl halides in DMSO. 

Anilines with strongly electron-withdrawing groups or diarylamines [38] are only weak nucleophiles, and might require deprotonation to react with electrophiles at acceptable rates (Scheme 6.8). These anilines can also be allylated by allyl palladium complexes [34], Electron-deficient anilines are electrophiles themselves, and can transfer the aryl group to other nucleophiles by aromatic nucleophilic substitution [39]. 

Studies (2, 3) have also been reported of the reaction of phosphorus trichloride with diarylamines containing p-methyl or p-chloro substituents. In every case, the expected ring-substituted derivatives of 1 and 2 were obtained after the reaction mixture was treated with water. The interaction of (V-phenyl-o-toluidine and phosphorus trichloride at 200°C also gave a reaction mixture from which the expected phosphine oxide was isolated (3). None of the corresponding spirophosphonium chloride, however, could be obtained. The failure to isolate this substance can not be explained simply by the presence of an ortho substituent in the diarylamine, since it had been previously found that a 34% yield of a spirophosphonium chloride can be obtained via the interaction of fl/-phenyl-l-naphthylamine and phosphorus trichloride (2). No dihydropheno-phosphazine derivatives at all were obtained by the interaction of di-o-tolylamine and phosphorus trichloride at 200°C (3). 

The present paper is concerned with the reaction between phosphorus trichloride and the meta-substituted diarylamines listed in Table I. The... 

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]. 

Aminations of five-membered heterocyclic halides, such as furans and thiophenes, are limited. These substrates are particularly electron-rich. As a result, oxidative addition of the heteroaryl halide and reductive elimination of the amine are slower than for simple aryl halides (see Sections 4.7.1 and 4.7.3). In addition, the amine products can be air-sensitive and require special conditions for their isolation. Nevertheless, Watanabe has reported examples of successful couplings between diarylamines and bromothiophenes [126]. Triaryl-amines are important for materials applications because of their redox properties, and these particular triarylamines should be especially susceptible to electrochemical oxidation. Chart 1 shows the products formed from the amination of bromothiophenes and the associated yields. As can be seen, 3-bromothiophene reacted in higher yields than 2-bromothiophene, but the yields were more variable with substituted bromothiophenes. In some cases, acceptable yields for double additions to dibromothiophenes were achieved. These reactions all employed a third-generation catalyst (vide infra), containing a combination of Pd(OAc)2 and P(tBu)3. The yields for reactions of these substrates were much higher in the presence of this catalyst than they were in the presence of arylphosphine ligands. 

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>. 

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... 

The major pathways for the anodic oxidation of diarylamines are N,N- or aryl,aryl-coupling, A,aryl-coupling, and nucleophilic substitution in the aromatic ring. Which pathway actually will be followed depends on the reaction conditions and the substitution pattern of the substrate. With regard to the latter, one has to distinguish between p-unsubstituted, p-mono- and / -disubstituted diphenylamines. 

Queiroz synthesized diarylamines in the benzothiophene series, where the ligand BINAP was used to achieve the Pd-catalyzed amination in medium to high yields [156]. The diarylamines 96 were used in materials with electronic or luminescent properties. These compounds were further cyclized to provide substituted thienocarbazoles, which are bioisosteres of natural antitumoral DNA intercalating compounds. The presence of fluorine atoms increased the solubility of these molecules [156]. 

The efficiency of the arylation is very dependent upon the basicity of the amines. Electron-poor anilines do not react, while electron-rich anilines give high yields of -arylation products. However, in the case of easily oxidised anilines, oxido-reduction of the aryllead reagent can compete with the 7V-arylation when the steric compression becomes too important. For example, in the case of mesitylamine (101), the copper-catalysed reaction with a variety of substituted phenyllead derivatives led to generally high yields of the diarylamines. 

It is clear that the ortho and para substituted diarylamines 16 and 17 are derived from capture of the singlet nitrene and the product of benzylic CH insertion 15 can be formed from either the triplet or singlet state of the nitrene. Decafluoroazobenzene is derived from a dimerization reaction of the triplet nitrene and pentafluoroaniline is formed by hydrogen atom abstraction reactions of triplet pentafluorophenyl nitrene, and possibly by some photoreduction of an excited state of the azide. It is clear from this data that the singlet and triplet nitrene are not rapidly interconverting, and there is no evidence for uphill intersystem crossing from the triplet to the singlet nitrene. 

The A-substituted 5,10-dihydrophenarsazines (122) and (123) are not accessible from A-sub-stituted diarylamines by the Wieland-Rheinheimer method, and therefore they have to be prepared via the anions of (121) (Scheme 21). Thus, Gavrilov has described the alkylation of the MgBr salt of (121), yielding (122) <87ZOB347>, while the 5,10-diphenyl compound (123) was obtained for the first time by the reaction of bromobenzene with the sodium salt of (121 R = Ph) in liquid ammonia <88JHC1555>. 

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