Arylamines yield

Secondary alkylamines and secondary arylamines yield A/-nitroso amines. 

As discussed in Section 7.4.2.5, the reduction of tetrazolium salts to formazans often results in further reduction products. As seen in Scheme 24, reduction of formazans with ammonium sulfide leads to the hydrazidine 161. The reduction can proceed further eliminating an arylamine, yielding an amidrazone, e.g., 162.364 By contrast, alcoholic hydrogen sulfide attacks... 

According to this mechanistic conception, jr-donor substituted nitrosoarenes exhibit a strong correlation between sulfenamide and arylamine yield, respectively, and the thiol concentration employed38,56. In the case of nitrosobenzene and 4-chloronitrosobenzene, however, the 1-thioglycerol proportion (1 2 and 1 25, respectively) had virtually no effect on the sulfinamide/sulfenamide ratio at pH 6-938. As to our understanding, this effect lacks any reasonable explanation. 

The salts (298) " undergo a nucleophilic displacement with arylamines, yielding intermediate tetrafluoroborates, which with ethanolic sodium hydroxide yield red meso-ionic l,2,3,4-thiatriazol-5-imines (299). The dipole moment of the diphenyl derivative in benzene is 3.7 D. ... 

In the presence of MgX2, organo-cadmium and -zinc compounds add smoothly to imines derived from aromatic aldehydes and arylamines. Yields are very low with isolated alkyl-cadmiums or -zincs which lack a Lewis acid promoter (equation 48). ... 

Reaction of dimethyl l,2,4,5-tetrazine-3,6-dicarboxylate with dimethylamine affords methyl 5-(methylamino)-l,2,4-triazinc-3-carboxylate (12), while reaction with arylamines yields pyra-zolo[3,4-( ]-l,2,4-triazines 13. Mechanisms for the formation of the two products have been suggested.231... 

Primary arylamines yield acridines 17 (Ullmann synthesis) by condensation with aldehydes in the presence of strong mineral acids (H2SO4, HCl) followed by dehydrogenation ... 

Further classes of A -thiazolines have been produced by Hantzsch s synthesis they include 3,4,5-trisubstituted 2-thio-A -thiazolines, 2-aryl-imino-3-aryl-4-methyl-A -thiazolines, 2-arylimino-3-diphenylphosphinyl-amino-A -thiazolines, 3,4-diaryl-2-[(arylsulphonyl)cyanomethylene]-A -thiazolines, and their 2-[(carbonamido)cyanomethylene] analogues. The interaction of phenacyl thiocyanate (163) and arylamines yields 2-imino-3-aryl-4-phenyl-A -thiazolines (165). The parallel intramolecular cyclization of (163) to 2-hydroxy-4-phenylthiazole (164) is not significant... 

Diazotization of a primary arylamine followed by treatment of the diazo mum salt with copper(l) bromide or copper(l) chloride yields the corre spending aryl bromide or aryl chloride... 

Many azo dyes, such as tartrazine (Section 4.04.4.1.3), are susceptible to reduction by bacterial reductases in the intestinal flora. Azo reduction is believed to proceed through a hydrazo intermediate that undergoes subsequent reductive cleavage of the nitrogen-nitrogen bond to yield the arylamine derivatives (B-80MI40406). 

The submitters have found that other arylamines may be employed in a similar manner in place of aniline. Thus N-2-cyanoethyl-/)-anisidine was obtained in 76% yield as plates,... 

Aryl isothiocyanates can be prepared by the action of thio-phosgene on the arylamine (this reaction fails with naphthyl compounds), by fission of a 5ym-diaryIthiourea with acidic reagents (this reaction involves the loss of half the amine used), and by the decomposition of an ammonium aryldithiocar-bamate (low yields are reported for naphthyl and other compounds).The procedure described here is that of Baxter, Cymerman-Craig, Moyle, and White. ... 

The Conrad-Limpach reaction is a sequence of the following reactions (a) condensation of an arylamine 1 with the ketone or aldehyde of a 3-ketoester or a-formylester 2 providing enamine 3, and (b) cyclization with loss of alcohol to yield 4-hydroxy-quinoline 4. 

More importantly, Peet and coworkers reported the reaction of o-nitroaniline 35 with acetylene dicarboxylate 32 to provide fumarate 36. Subsequent cyclization proved difficult under thermal conditions and only a 35% yield of quinolone 37 was isolated. Use of PPA for the cyclization improved the yield of 37 significantly. Using this modification allowed enamino-ester formation with a nitro-group attached to the arylamine. 

Heating arylamines with carbon dioxide at 200 C (8500 atm) gives good yields of 3-aryl derivatives of 2,4-dihydroxyquinazoline ° (see 5e). The method is unsatisfactory when riitro, halo, and phenolic anilines and a- or p-naphthylamines are used. 

Another short protocol for preparation of 3 was recently presented by Knolker and Reddy, who devised a short sequence involving a double iron-mediated arylamine cyclization as the key step (Scheme 19). Thus, the reaction of m-phenylenediamine (140) with the tricarbonyliron-complexed cyclohexadienyl cation 141 yielded the complex 142, which was eventually transformed into indolo-[2,3-()]carbazole (3) via cyclization and dehydrogenation (98TL4007 00T4733). 

The synthesis can be conducted both in solution and without solvents. The reaction in solvent (e.g., methanol, ethanol, dioxane, dimethylformamide) is recommended for volatile 1,3-diynes and amines in this case the pyrroles are purer and the yield is higher. With disubstituted diacetylenes, ammonia and primary alkyl- and arylamines produce 1,2,3-trisubstituted pyrroles under the same conditions (65CB98 71MI1). Since disubstituted diacetylenes are readily obtained by oxidative coupling of acetylenes (98MI2), this reaction provides a preparative route to a wide range of pyrroles. 

The work of Greenfield and Malz (25) on the preparation of arylamines illustrates the sensitivity of yield to hindrance and an influence of catalyst. 

Primary arylamines react with nitrous acid, HNO2, to yield stable arenediazonium +... 

Arenediazonium salts undergo a coupling reaction with activated aromatic rings such as phenols and arylamines to yield brightly colored azo compounds, Ar—N=N—Ar. ... 

Pioneering studies have shown that the yield of iV-phenyl-3//-azepin-2-amine (32, R = Ph) from the thermolysis of phenyl azide in aniline increases as the ratio of azide to aniline decreases, and in dilute solution with an azide to aniline ratio of 1 200 a 54% yield of the 3//-azepine can be achieved.34 The reaction is successful with other arylamines, but the procedure is of limited preparative value as large volumes of amine are required and only moderate yields of 3H-azepines are obtained. 

The yield of 3//-azepine appears to be influenced by substituents on the azide ring although no in-depth study has been reported. 4-Halophenyl azides, in most cases, give rise to complex mixtures of products.177 4-Tolyl azide, on thermolysis in aniline, yields 5-methyl-iV-phenyl-3//-azepin-2-amine (18% mp 157-158°C), whereas the thermolyses of 4-methoxy-, 4-methyl-, 4-chloro-, and 4-nitrophenyl azides in a range of arylamines (4-chloro-, 4-methoxy-, and pen-tafluoroaniline) yield only azo compounds and uncharacterized tarry products.178... 

The structure of the tar, formed in many azide decompositions, consists of polyazepine units,103 and arises by attack of arylamine, formed from triplet arylnitrene, on the azepine precursor 30 to give the l//-azcpin-2-amine 31, which acts as a nucleophile towards more azepine precursor to yield ultimately the polyazepine 95. 

Singlet phenylnitrene, and hence /V,A -diethyl-3//-azcpin-2-amines, e. g. 102, can be generated by the thermolysis of A,-phenyl-Af,<9-bis(trimcthylsi]yl)hydroxylamine (100) in the presence of dialkylamines the reaction fails, however, with arylamines.210 Photofragmentation of the spiro oxaziridine 101 in diethylamine solution also produces the 3//-azepine 102,2,1 and an oxaziridine intermediate is probably involved in the formation, in low yield (1 %), of azepine 102 by the photolysis of A/,A( -diarylbenzoquinonc diimine A/,A/ -dioxides in benzene/die-thylamine solution.212... 

Replacement of the carbaldehyde function by other carbonyl groups is successful and leads to the formation of bcnzazcpincs bearing additional substituents at the 1- and 5-positions.100 For example, 1,2-dibenzoylbenzene (69) and TV.A -bisIcyanomethyOisopropylamine yield the pentasubstituted 3/7-3-benzazcpinc 70. However, condensations with other bis(cyanomethyl)-alkylamines and with bis(cyanomethyl)arylamines produce only acyclic condensation products. 

Research into the mechanism of diazotization was based on Bamberger s supposition (1894 b) that the reaction corresponds to the formation of A-nitroso-A-alkyl-arylamines. The TV-nitrosation of secondary amines finishes at the nitrosoamine stage (because protolysis is not possible), but primary nitrosoamines are quickly transformed into diazo compounds in a moderately to strongly acidic medium. The process probably takes place by a prototropic rearrangement to the diazohydroxide, which is then attacked by a hydroxonium ion to yield the diazonium salt (Scheme 3-1 see also Sec. 3.4). 

The Pd°-catalyzed arylations using arenediazonium tetrafluoroborates are limited to those diazonium salts that can be manipulated at room temperature. The reaction can, if necessary, be performed at temperatures up to 50 °C by using a mixture of an arylamine and tert-butyl nitrite in chloroacetic acid or in a mixture of chloroacetic and acetic acid (Kikukawa et al., 1981a). Styrene reacted with fourteen arylamines in the presence of 5 mol-% Pd(dba)2 to give the corresponding substituted stilbenes in yields of 46-97%. It is important for good yields to carry out these reactions in an acidic system. Without acid the yield was low (11%), and diazo tars were also formed. 

With regard to the mechanism of these Pd°-catalyzed reactions, little is known in addition to what is shown in Scheme 10-62. In our opinion, the much higher yields with diazonium tetrafluoroborates compared with the chlorides and bromides, and the low yields and diazo tar formation in the one-pot method using arylamines and tert-butyl nitrites (Kikukawa et al., 1981 a) indicate a heterolytic mechanism for reactions under optimal conditions. The arylpalladium compound is probably a tetra-fluoroborate salt of the cation Ar-Pd+, which dissociates into Ar+ +Pd° before or after addition to the alkene. An aryldiazenido complex of Pd(PPh3)3 (10.25) was obtained together with its dediazoniation product, the corresponding arylpalladium complex 10.26, in the reaction of Scheme 10-64 by Yamashita et al. (1980). Aryldiazenido complexes with compounds of transition metals other than Pd are discussed in the context of metal complexes with diazo compounds (Zollinger, 1995, Sec. 10.1). 

This procedure is a general way of converting arylamines to aryl fluorides, for it has been used to make fifteen other aryl fluorides. It generally gives better yields than the Schiemann reaction. 

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