Amines reaction with arenes

Unlike most of the other oxidative reactions developed in our group, the I(III)-mediated amination did not require the arene reagent to be used as a solvent. Near 1 1 ratios of the N-H and the C-H substrate could be used. Unfortunately, the metal-free amination provided intractable mixmres of products with monosubstituted and nonsymmetric arene substrates (Scheme 9). This problem was exemplified by the amination of toluene, which produced three regiomers in a 10 6 5 (ortho/meta/para) ratio. We demonstrated the application of the metal-free amination reaction with 18 substrates, but all nonsymmetric arenes produced complex mixtures of aminated products. " ... 

Combined effect of BTMA Br3 and ZnCl2 in acetic acid provides a new excellent bromination procedure for arenes. That is, while such reactive aromatic compounds as phenols, aromatic amines, aromatic ethers, and acetanilides have been easily brominated by BTMA Br3 in dichloromethane in the presence of methanol, the reaction of arenes, less reactive compounds, with BTMA Br3 in dichloromethane-methanol did not proceed at all, even under reflux for many hours. However, arenes could be smoothly brominated by use of this agent in acetic acid with the aid of the Lewis acid ZnCl2 (Fig. 13) (ref. 16). 

Fagnou and co-workers reported on the use of a palladium source in the presence of different phosphine ligands for the intramolecular direct arylation reaction of arenes with bromides [56]. Later, they discovered that new conditions employing palladium complex 27 promoted the direct arylation of a broad range of aryl chlorides to form six- and five-membered ring biaryls including different functionalities as ether, amine, amide and alkyl (Scheme 7.11) [57]. 

Arylamines and hydrazines react with tosyl azide under basic conditions to yield aryl azides [1] and arenes [2], respectively, by an aza-transfer process (Scheme 5.25). Traditionally, the reaction of anilines with tosyl azides requires strong bases, such as alkyl lithiums, but acceptable yields (>50%) have been obtained under liquidiliquid phase-transfer catalytic conditions. Not surprisingly, the best yields are obtained when the aryl ring is substituted by an electron-withdrawing substituent, and the yields for the corresponding reaction with aliphatic amines are generally poor (-20%). Comparison of the catalytic effect of various quaternary ammonium salts showed that tetra-/i-butylammonium bromide produces the best conversion, but differences between the various catalysts were minimal [ 1 ]. 

Electron-rich carbyne complexes can react at the carbyne carbon atom with electrophiles to yield carbene complexes. Numerous examples of such reactions, mostly protonations, have been reported [519]. Depending on the nucleophilicity of the carbyne complex, such reactions will occur more or less readily. The protonation of weakly nucleophilic carbyne complexes requires the use of strong acids, such as triflic [533], tetrafluoroboric [534] or hydrochloric acid [535,536]. More electron-rich carbyne complexes can, however, even react with phenols [537,538], water [393,539], amines [418,540,541], alkyl halides, or intramolecularly with arenes (cyclometallation, [542]) to yield the corresponding carbene complexes. A selection of illustrative examples is shown in Figure 3.25. 

Success was obtained with Ru3(CO)i2 as catalyst precursor [6], but the most efficient catalysts were found in the RuCl2(arene)(phosphine) series. These complexes are known to produce ruthenium vinylidene spedes upon reaction with terminal alkynes under stoichiometric conditions, and thus are able to generate potential catalysts active for anti-Markovnikov addition [7]. Similar results were obtained by using Ru(r]" -cyclooctadiene)(ri -cyclooctatriene)/PR3 as catalyst precursor [8]. (Z)-Dienylcarba-mates were also regio- and stereo-selectively prepared from conjugated enynes and secondary aliphatic amines (diethylamine, piperidine, morpholine, pyrrolidine) but, in this case, RuCl2(arene) (phosphine) complexes were not very efficient and the best catalyst precursor was Ru(methallyl)2(diphenylphosphinoethane) [9] (Scheme 10.1). 

As with arene-amine radical ion pairs, the ion pairs formed between ketones and amines can also suffer a-deprotona-tion. When triplet benzophenone is intercepted by amino acids, the aminium cation radical can be detected at acidic pH, but only the radical formed by aminium deprotonation is detectable in base (178). In the interaction of thioxanthone with trialky lamines, the triplet quenching rate constant correlates with amine oxidation potential, implicating rate determining radical ion pair formation which can also be observed spectroscopically. That the efficiency of electron exchange controls the overall reaction efficiency is consistent with the absence of an appreciable isotope effect when t-butylamine is used as an electron donor (179). 

Ozonium Ion (H03+). Ozone is a resonance hybrid of canonical structures 50a-50d.135 Ozone does in fact act as a 1,3-dipole—that is, either as an electrophile or a nucleophile. The electrophilic nature of ozone has been recognized for a long time in its reactions with alkenes, alkynes, arenes, amines, phosphines,... 

The isocyanate can be replaced by the corresponding activated urethane (as a milder reagent), and this activation can also involve the p-amino functions of the calix[4]arene (step e) and their subsequent reaction with a suitable amine (step f). Multigram quantities of simple tetra-urea calix[4]arenes are easily available in this way. 

Synthetically useful reactions of (arene)Mn(CO)3+ complexes with such nucleophiles as methoxide, benzenethiolate, azide, various amines, and anilines are also noteworthy. These complexes have also been extensively studied with regard to nucleophilic addition reactions resulting in thermally stable cyclohexadienyl complexes [2]. 

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