Ortho-substituted aniline

There are relatively few methods available for the preparation of condensed 1,2,3-triazines. By far the most commonly employed procedure is diazotization of a suitably ortho-substituted aniline (4) or amino-substituted heterocycle of the type 5, and examination of the different X substituents which have been used successfully in this synthesis reveals... 

There are a number of important reactions in this category and all of them involve at least one heteroatom functioning as a nucleophile and another as an electrophile. Diazo-tization of a variety of ortho-substituted anilines for instance, followed by intramolecular nucleophilic trapping of the corresponding diazonium salts by either nitrogen or carbon nucleophiles, is the basis of a series of very important syntheses of 1,2,3-benzotriazine and cinnoline derivatives, and this general approach has been widely exploited for the preparation of polycyclic systems. Representative examples are given in equations (51)—(54). 

Correlation with Hammett substituent constants alone was not satisfactory. The reaction has been extended to ortho substituted anilines also the results have been treated by the Fujita-Nishioka method. Combining these with the previous data for meta and para substituted anilines, a multiparameter regression equation (2) has been developed (79JCS(P2)219>. 

We have developed a multimetallic catalyst for the large scale synthesis of sterically hindered mono-N-alkylanilines with very good selectivity and high catalytic activity. In contrast to copper chromite catalysts which allow the N-alkylation only with primary alcohols, the doubly promoted Pt/Si02 catalysts described here are useful for the reaction of ortho-substituted anilines with both primary and secondary alcohols. 

Ring closure of ortho-substituted /-anilines, lor heleroeycles, 14, 211... 

Anilines are readily oxidized by DIB, being converted either into azo compounds or into other products of condensation, in complex solvent-dependent reactions without much synthetic utility. Better results were obtained in some intramolecular cyclizations of 2,2-diamino-diarylmethanes and 2,2-diamino-diarylsulphones, which afforded the corresponding cyclic azo compounds (diazepines) [50,51], More generally, intramolecular cyclizations of ortho-substituted anilines are known to occur on oxidation of several substrates, according to the following scheme [52] ... 

Heterocycles by Ring Closure of Ortho-Substituted /-Anilines (The /-Amino Effect)... 

The dibenzo- 1,5-oxazocine 540 was obtained, in nearly quantitative yield, via intramolecular carbonylation of ortho-substituted aniline 539 with 100 psi CO in the presence of recyclable palladium-complexed dendrimer on silica (Gl-Pd) as catalyst and diisopropylethylamine (DIPEA) (Equation 23) <2005JA14776>. 

In 1964, Lady and Whetsel focused on the problem of the first overtone N—H stretching bands of 52 ortho-substituted anilines, in cyclohexane and in CCI4, in order to evaluate the intramolecular hydrogen bond between N—H and ortho substituents54. The N—H stretching frequencies in ortho-substituted anilines have also been discussed by G. Moritz55. 

In the same year, Krueger studied the intramolecular hydrogen bonding interaction in 31 ortho-substituted anilines and their NHD and ND2 isotopomers56. In fact, the first overtone NH2 symmetric stretching band is independent of the concentration of aniline and of temperature. A strong intramolecular hydrogen bond is supported also by spectral data of ortho-substituted tV-methylanilines and ND IV-methylanilines. 

Buchwald has also shown that the easily synthesized DPEphos ligand is an ideal catalyst for the arylation of anilines with aryl bromides.24 Even di-ortho substituted aniline and aryl bromide can be efficiently coupled. Furthermore, Buchwald has reported that readily available, and cheaper, PdCl2 may serve as the Pd source rather than Pd(OAc)2. 

Figure 8. Correlation of EOI with the substituent constant a of ortho-substituted anilines. Conditions as in Fig. 7...

There are several methods reported in the literature for the oxidation of aniline, which include (i) the use of MnOs to produce azobenzene, (ii) the use of aqueous peracids to oxidize ortho-substituted aniline to nitrobenzene, (iii) the use of aqueous peracids to oxidize non-substituted anilines to azo- and azoxybenzene, (iv) the use of anhydric peracids to produce the corresponding nitrobenzenes, and (v) the use of catalytic systems, such as t-BuOjH-MoCVI), V(V), or t-BuOjH-TiCIV), to produce nitrobenzene or azoxybenzene. 

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