Anilines, substituted, reaction with

Pyrroles are exceptionally nucleophilic heterocycles and undergo electrophilic substitution reactions with very weak electrophiles. The reactivity of pyrrole may be compared with that of N,(V-dimethyl-aniline or phenol all three compounds couple with the benzenediazonium ion. It is no surprise, therefore, that Mannich reactions of pyrrole and substituted pyrroles have been studied in considerable detail. We will concentrate our attention on recent studies. 

Indole-3-carboxylate esters and 3-acetylindoles can be prepared by palladium-catalyzed cycli-zation of enamines (14). These can be prepared from the corresponding anilines by condensation with j8-dicarbonyl compounds or by palladium-catalyzed substitution reactions with ethyl acrylate or methyl vinyl ketone <86BCJ927, 90S215>. Overall yields for the two-step process are 60-80% (Scheme 33). 

In addition to being used to synthesize substituted benzenes, arenediazonium ions can be used as electrophiles in electrophilic aromatic substitution reactions. Because an arenediazonium ion is unstable at room temperature, it can be used as an electrophile only in reactions that can be carried out well below room temperature. In other words, only highly activated benzene rings (phenols, anilines, and N-alkylanilines) can undergo electrophilic aromatic substitution reactions with arenediazonium ion electrophiles. The product of the reaction is an azo compound. The N=N linkage is called an azo linkage. 

The t-butoxycarbonyl group also favours o-lithiation as in N-(t-butoxy-carbonyl)aniline subsequent reaction with electrophiles provides a route to o-functionalized anilines.Pyridines substituted at the 2- or 3-positions with dialkylcarboxylic acid amides and halogens undergo regiospecific lithiation and then electrophilic attack. In both cases the 2-substituent gives reaction at the 3-position, whereas the 3-substituted pyridine undergoes attack exclusively at the 4-position. The o-lithiated benzamide (15) has been used in the synthesis of polycyclic aromatic hydrocarbons and ellipticine alkaloids by reaction with aromatic aldehydes. ... 

Four nucleophilic aromatic substitution reactions with amines have been studied for deuterium isotope effects. Hawthorne (81) found that the rates of reaction of o- and p- nitrochlorobenzene with piperidine in xylene are not altered by substitution of deuterium for hydrogen on the amino group of the nucleophile. Similarly, 2,4-dinitrochlorobenzene reacts at identical rates with -butylamine and with iV,iV-dideuterio-n-butylamine containing 0.75% ethanol (76). Under the conditions of the rate measurements the deuterated amine does not undergo exchange with either the chloroform or the ethanol present. Finally, the reaction of trichloro-s-triazene with aniline shows no isotope effect with AT,JV-dideuterioaniline in benzene as well as in benzene saturated with deuterium oxide (82). 

The success of the Bart reaction when applied to nuclear- substituted anilines is often much affected by the pH of the reaction-mixture. Furthermore, the yields obtained from some m-substituted anilines, which under the normal conditions are usually low, arc considerably increased by the modifications introduced by Scheller, and by Doak, in which the diazotisation is carried out in ethanolic solution followed by reaction with arsenic trichloride in the presence of a cuprous chloride or bromide catalyst. 

The diazonium salts 145 are another source of arylpalladium com-plexes[114]. They are the most reactive source of arylpalladium species and the reaction can be carried out at room temperature. In addition, they can be used for alkene insertion in the absence of a phosphine ligand using Pd2(dba)3 as a catalyst. This reaction consists of the indirect substitution reaction of an aromatic nitro group with an alkene. The use of diazonium salts is more convenient and synthetically useful than the use of aryl halides, because many aryl halides are prepared from diazonium salts. Diazotization of the aniline derivative 146 in aqueous solution and subsequent insertion of acrylate catalyzed by Pd(OAc)2 by the addition of MeOH are carried out as a one-pot reaction, affording the cinnamate 147 in good yield[115]. The A-nitroso-jV-arylacetamide 148 is prepared from acetanilides and used as another precursor of arylpalladium intermediate. It is more reactive than aryl iodides and bromides and reacts with alkenes at 40 °C without addition of a phosphine ligandfl 16]. 

Dijbner-von Miller Synthesis. A much less violent synthetic pathway, the Dn bner-von Miller, uses hydrochloric acid or 2inc chloride as the catalyst (43). As in the modified Skraup, a,P-unsaturated aldehydes and ketones make the dehydration of glycerol uimecessary, and allow a wider variety of substitution patterns. No added oxidant is required. With excess aniline the reaction proceeds as follows ... 

The reaction of substituted chloronitrobenzenes with arylamines to form substituted diphenyl amines is typified by 4-rutrodiphenylamine-2-sulfoiiic acid where 4-chloronitrobenzene-3-sulfonic acid (PN salt) is condensed with aniline ia an aqueous medium at 120°C and 200 kPa (2 atm) ia the presence of alkaline buffer at low pH to avoid the competing hydrolysis of the PN salt. 

Because of the structural requirements of the bielectrophile, fully aromatized heterocycles are usually not readily available by this procedure. The dithiocarbamate (159) reacted with oxalyl chloride to give the substituted thiazolidine-4,5-dione (160) (see Chapter 4.19), and the same reagent reacted with iV-alkylbenzamidine (161) at 100-140 °C to give the 1 -alkyl-2-phenylimidazole-4,5-dione (162) (see Chapter 4.08). Iminochlorides of oxalic acid also react with iV,iV-disubstituted thioureas in this case the 2-dialkylaminothiazolidine-2,4-dione bis-imides are obtained. Thiobenzamide generally forms linear adducts, but 2-thiazolines will form under suitable conditions (70TL3781). Phenyliminooxalic acid dichloride, prepared from oxalic acid, phosphorus pentachloride and aniline in benzene, likewise yielded thiazolidine derivatives on reaction with thioureas (71KGS471). 

These Br nsted-type plots often seem to be scatter diagrams until the points are collated into groups related by specific structural features. Thus, p-nitrophenyl acetate gives four separate, but parallel, lines for reactions with pyridines, anilines, imidazoles, and oxygen nucleophiles.Figure 7-4 shows such a plot for the reaction of trans-cmmm c anhydride with primary and secondary aliphatic amines to give substituted cinnamamides.All of the primary amines without substituents on the a carbon (R-CHi-NHi) fall on a line of slope 0.62 cyclopentylamine also lies on this line. If this line is characteristic of normal behavior, most of the deviations become qualitatively explicable. The line drawn through the secondary amines (slope 1.98) connects amines with the structure R-CHi-NH-CHi-R. The different steric requirements in the acylation reaction and in the model process... 

In 1904, Zincke reported that treatment of Al-(2,4-dinitrophenyl)pyridinium chloride (1) with aniline provided a deep red salt that subsequently transformed into A-phenyl pyridinium chloride 5 (Scheme 8.4.2). Because the starting salt 1 was readily available from the nucleophilic aromatic substitution reaction of pyridine with 2,4-dinitrochlorobenzene, the Zincke reaction provided access to a pyridinium salt (5) that would otherwise require the unlikely substitution reaction between pyridine and... 

The electronic properties of the aniline are important in the Doebner reaction. The reaction works best with electronic donating groups. Anilines substituted with a chlorine at the meta position consistently give low yields, but fluorine at the meta position seems... 

A similar substitution reaction occurs with other strong bases. Treatment of bromobenzene with potassium amide (KNH2) in liquid Nhh solvent, for instance, gives aniline. Curiously, though, when bromobenzene labeled with radioactive 14C at the Cl position is used, the substitution product has equal amounts of the label at both Cl and C2, implying the presence of a symmetrical reaction intermediate in which Cl and C2 are equivalent. 

It has already been pointed out that nitrosation is probably the first step in diazotization. Ingold (1952) describes the reaction as N-nitrosation and classifies it as an electrophilic substitution, together with related processes such as the formation of 4-nitrosophenol, an example of a C-nitrosation. It was probably Adamson and Kenner (1934) who first applied these ideas to diazotization and realized that in aniline itself the electron density at the nitrogen atom is greater than in the anilinium ion, so that the base is more reactive. On the other hand, the nitrosoacidium ion (3.1), the addition product of nitrous acid and a proton, is a more powerful electrophilic reagent than the HN02 molecule. They therefore represented the first step of diazotization as in Scheme 3-5. 

It has been shown that the imidoyl chloride moiety of 2(lff)-pyrazinones can imdergo an easy addition/elimination reaction with alkyl amines [24], while reactions with anilines proceed under harsher conditions. Ullmann coupling [109-113] of 2(lff)-pyrazinones with substituted anilines could open the way to the libraries of physiologically active compounds useful in inhibiting HIV replication [7]. Polymer-bound pyrazinone was successfully... 

When p-ethylaminobenzoate and N,N-dimethyl-p-phenylene diamine sulfate were similarly treated with the dibromosulfone (I) for 2 h, the yield was only 32% and 15% respectively (Figure 1). A possible explanation is that the nucleophilicity of these monosubstituted anilines is weaker than that of aniline while a Na2C03 1,4-HBr elimination reaction could be competing with the substitution reaction, leading to the lower yield (18). 

The synthesis of nitro dyes is relatively simple, a feature which accounts to a certain extent for their low cost. The synthesis, illustrated in Scheme 6.5 for compounds 140 and 141, generally involves a nucleophilic substitution reaction between an aromatic amine and a chloronitroaromatic compound. The synthesis of C. I. Disperse Yellow 14 (140) involves the reaction of aniline with l-chloro-2,4-dinitroaniline while compound 141 is prepared by reacting aniline (2 mol) with compound 144 (1 mol). 

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