Anilides, arylation

Sanford has reported a method for palladium-catalyzed anilide arylation by iodonium salts (Scheme 10) [51]. The reactions proceed by a Pd(II)-Pd(IV) couple mechanism. High functional group tolerance, excellent regioselectivity, and good reaction scope was observed. The reactions were carried out at 100 °C in acetic acid solvent. 

Several reports have appeared describing anilide arylation by arenes that do not involve coupling of a C-H bond with a C-Hal bond and thus will be discussed only briefly. Buchwald has shown that oxidative arylation of anilides takes place in presence of 5-10 mol% of palladium acetate and catalytic DMSO in trifluoroacetic acid solvent by using oxygen as the terminal oxidant [52], Pivalanilides afford the best results. Notably, only about four equivalents of the arene component are required for efficient arylation. However, regioisomer mixtures were obtained if monosubstituted arenes were used as the coupling components. 

We reasoned that the arylation of benzamide derivatives should also be possible under Pd(II)-Pd(IV) couple conditions. Gratifyingly, conditions that were developed for anilide arylation worked well for benzamide arylation (Scheme 12) [57],... 

According to mechanistic considerations of Scheme 8, benzylamine arylation should also be feasible. The palladation of benzylamines in strong acid might be retarded due to protonation of the directing amino group. Employing a limited amount of trifluoroacetic acid solvent allowed efficient benzylamine arylation [63], Specifically, the benzylamine arylation reactions are the fastest if about five equivalents of trifluoroacetic acid solvent are used. A number of benzylamines and A-methy lbenzy I am i n e s were shown to be reactive under these conditions (Scheme 16). The reactions proceed well with both electron-rich and moderately electron-poor benzylamines. For unsubstituted or 4-substituted benzylamines, 2,6-diarylation is observed. Benzylamines substituted at the 3-position are monoarylated. As in the case of pyridine and anilide arylation, bromine is tolerated on the substrate, and even iodide is compatible with the reaction conditions, although the yield is reduced. The products are acylated after the reaction to facilitate isolation. 

The Knorr quinoline synthesis refers to the formation of a-hydroxyquinolines 4 from P-ketoesters 2 and aryl amines 1. The reaction usually requires heating well above 100°C. However, some cases do exist when the cyclization takes place in the presence of a catalytic amount of mineral acid at temperatures as low as -10 °C. The intermediate anilide 3 undergoes cyclization by dehydration with concentrated sulfuric acid. The reaction is conceptually close to the Doebner-Miller and Gould-Jacobs reactions. ... 

A variety of aryl systems have been explored as substrates in the Knorr quinoline synthesis. Most notable examples are included in the work of Knorr himself who has demonstrated the high compatibility of substituted anilines as nucleophilic participants in that reaction. In the case of heteroaromatic substrates however, the ease of cyclization is dependent on the nature and relative position of the substituents on the aromatic ring." For example, 3-aminopyridines do not participate in ring closure after forming the anilide... 

Most of the subsequent work on this reagent was concerned with the formation of aryl radicals (see review by Cadogan, 1971). However, 2-terf-butyl-A-nitrosoacet-anilide was found to decompose in benzene to give, instead of 2-tert-butylbiphenyl, as expected for a substitution of benzene by a 2-tert-butylphenyl radical, a mixture of isomeric tert-butylphenyl acetates. A careful reexamination (Cadogan and Hib-bert, 1964) suggested that the ratio of 2- and 3-tert-butylphenyl acetates was consistent with the involvement of 2-tert-butylbenzyne, i.e., the product of an ionic dediazoniation, as an intermediate. This was later confirmed by trapping experiments designed to detect aryne intermediates. 

It is intriguing to note that this reaction scheme for the reduction of a sulphone to a sulphide leads to the same reaction stoichiometry as proposed originally by Bordwell in 1951. Which of the three reaction pathways predominates will depend on the relative activation barriers for each process in any given molecule. All are known. Process (1) is preferred in somewhat strained cyclic sulphones (equations 22 and 24), process (2) occurs in the strained naphtho[l, 8-hc]thiete 1,1-dioxide, 2, cleavage of which leads to a reasonably stabilized aryl carbanion (equation 29) and process (3) occurs in unstrained sulphones, as outlined in equations (26) to (28). Examples of other nucleophiles attacking strained sulphones are in fact known. For instance, the very strained sulphone, 2, is cleaved by hydride from LAH, by methyllithium in ether at 20°, by sodium hydroxide in refluxing aqueous dioxane, and by lithium anilide in ether/THF at room temperature. In each case, the product resulted from a nucleophilic attack at the sulphonyl sulphur atom. Other examples of this process include the attack of hydroxide ion on highly strained thiirene S, S-dioxides , and an attack on norbornadienyl sulphone by methyllithium in ice-cold THF . ... 

Such reactions are also possible in vitro, as several mild oxidizing agents are at hand nowadays. Thus, the Dess-Martin periodinane (DMP) [50] has been proven to be a versatile and powerful reagent for the mild oxidation of alcohols to the corresponding carbonyl compounds. In this way, a series of new iodine(V)-mediated reactions has been developed which go far beyond simple alcohol oxidation [51], Ni-colaou and coworkers have developed an effective DM P-mediated domino polycy-clization reaction for converting simple aryl amides, urethanes and ureas to complex phenoxazine-containing polycycles. For example, reaction of the o-hydroxy anilide 7-101 with DMP (2 equiv.) in refluxing benzene under exposure to air led to polycycle 7-103 via 7-102 in a yield of 35 % (Scheme 7.28) [52]. 

Quinazolines 51 have been prepared by the condensation of A-aryl carbamates with hexamine, followed by aromatisation of the dihydro intermediate. A variety of mono- and di-substituted anilides were used, mefa-substituted starting materials giving 7-substituted quinazolines <06T12351>. Benzoquinazolines were also prepared similarly from naphthylamine carbamates <06OL255>. 

These pigments are obtained by coupling substituted aryl diazonium salts with ary-lides of 2-hydroxy-3-naphthoic acid (2-hydroxy-3-naphthoic acid anilide = Naph-tol AS). They provide a broad range of colors from yellowish and medium red to bordeaux, carmine, brown, and violet their solvent fastness and migration resistance are only marginal. Naphthol AS pigments are used mainly in printing inks and paints. 

Amide hydrolysis at alkaline pH involves a tetrahedral anionic intermediate, which was mimicked by the transition state analogue [49], an /V-aryl arylphosphonamidate, appropriately related to substrate anilide [50] (Fig. 18) (Appendix entry 2.8). 

These ideas will be discussed in the following subsections, where most of the attention will be devoted to the mechanistic smdies with aromatic esters, which have been the subject of an overwhelming majority of the research efforts. Nevertheless, the same reaction mechanism has been shown to be valid for the PFR of anilides, thioesters, sulfonates, and so forth. Furthermore, it is also applicable to the photo-Claisen rearrangement [i.e. the migration of alkyl (or allyl, benzyl, aryl,)] groups of aromatic ethers to the ortho and para positions of the aromatic ring [21,22]. 

Arsanilic acid was prepared by Bechamp 1 by heating aniline arsenate to 190-200°. The product was originally described as the anilide of arsenic acid, but Ehrlich and Bertheim 2 showed its structure to be that of a true aryl arsenic acid. 

Table 3.26 lists illustrative examples of cleavage reactions of support-bound N-aryl-carbamates, anilides, and /V-arylsulfonamidcs. /V-Arylcarbamatcs are more susceptible to attack by nucleophiles than /V-alkylcarbamates, and, if strong bases or nucleophiles are to be used in a reaction sequence, it might be a better choice to link the aniline to the support as an /V-bcnzyl derivative. Entry 7 (Table 3.26) is an example of a safety-catch linker for anilines, in which activation is achieved by enzymatic hydrolysis of a phenylacetamide to liberate a primary amine, which then cleaves the anilide. 

Pussemier et al. (1989) found that log Koc for 12 aryl N-methylcarbamates correlated significantly to a linear combination of two parameters, % hydrophobic effect (calculated from RP-HPLC measurements) and 8 Hildebrand solubility parameter. The authors also used data for 16 phenylureas and 13 anilides from Briggs (1981) and obtained similar results. 

Scheme 5. Effect of aryl substitution and method of preparation on anilide complexes...

V-Methyl a,(3-unsaturated anilides undergo intramolecular arylation exclusively at the a-position to afford 3-alkylideneoxindoles. The best results are obtained with KNH2/NH3 under photoinitiation (Sch. 44). 

An anionic ortho-Fries rearrangement has been used to make BINOL derivatives.194 2.3.2.1.5 Anilides and A-aryl carbamates... 

The recent literature presented some improvements of the known procedures rather than new synthetic approaches. An efficient and more sustainable protocol for the copper-catalysed intramolecular O-arylation of ortho-halo anilides to afford benzo[<7]oxazoles has been described. After an optimization process, the best conditions were the use of CuCl and TMEDA in water... 

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