Mesitylene, acylation

Arenediazonium ions are relatively weak electrophiles, and therefore react only with electron-rich aromatic substrates like aryl amines and phenols. Aromatic compounds like anisole, mesitylene, acylated anilines or phenolic esters are ordinarily not reactive enough to be suitable substrates however they may be coupled... 

In a comparative study on the acylation of mesitylene and anisole with BC, promoted by clayfen, - it is observed that mesitylene reacts faster (by a factor of three) when the reactions are carried out separately. However, when the two substrates are reacted jointly, competition favors anisole (by fhe same factor of three). A tentative explanation for this reversal activity can be based on the assumption that benzoylation of mesitylene and anisole follows fwo different mechanisms characterized by different levels of interaction of fhe catalysf surface with the aromatic substrate and the benzoyl cation. In particular, it must be taken into consideration that anisole interacts more strongly than mesitylene with the acid centers of the catalyst and, consequently, its intrinsic higher reactivity toward the acyl cation can be dramatically lowered, and the acid sites are less available for mesitylene acylation reaction. 

Similarly, A[-carboxy-a-amino acid anhydrides react with aromatics such as toluene, xylenes, and mesitylene to give a-amino acylated products ia moderate yields with almost complete retention of configuration of the a-amino acid. 

The ability of iron(III) chloride genuinely to catalyze Friedel-Crafts acylation reactions has also been recognized by Holderich and co-workers [97]. By immobilizing the ionic liquid [BMIM]Cl/FeCl3 on a solid support, Holderich was able to acetylate mesitylene, anisole, and m-xylene with acetyl chloride in excellent yield. The performance of the iron-based ionic liquid was then compared with that of the corresponding chlorostannate(II) and chloroaluminate(III) ionic liquids. The results are given in Scheme 5.1-67 and Table 5.1-5. As can be seen, the iron catalyst gave superior results to the aluminium- or tin-based catalysts. The reactions were also carried out in the gas phase at between 200 and 300 °C. The acetylation reac-... 

Table 5.1-5 The acylation of aromatics in batch reactions at 100 °C, for 1 hour. Ratio of aromatic compound to acetylating agent = 5 1, mes. = mesitylene.

In contrast to the acyl- and sulfonylnitrenes described in this section, arylnitrenes produced thermally or photolytically from aryl azides, including those bearing strongly electron-withdrawing substituents (e.g., CN, N02, CF3), fail to promote ring expansion of arenes to 1H-azepines, although intermolecular substitution of electron-rich substrates, e.g. mesitylene and A.TV-dimethylaniline, have been noted.167... 

In the reaction of 1-alkoxycarbonylimidazoles with 2-aminobenzimidazole at low temperature and short reaction time an acylation at the ring nitrogen was encountered. At higher temperature (refluxing mesitylene) and longer reaction time, however, the 2-amino group is acylated [222]... 

Electron-rich aromatic compounds such as durene, p-dimethoxybenzene, mesitylene, anisole, thiophene, and fluorene can be benzoylated or acetylated by the corresponding Af-acylimidazole in trifluoroacetic acid to give the corresponding benzophenone or acetophenone derivative in good yield (Method A). As the actual acylating agent, a mixed anhydride of trifluoroacetic acid and benzoic acid has been proposed 1973... 

The ionic liquids made of ferric chloride and tin chloride displayed good properties as alternative catalysts in the acylation reactions (127). For the acylation of mesitylene with acetylchloride and for the acylation of anisole with acetylanhydride, the best results were obtained with a ferric chloride-containing ionic liquid. The conversions were much higher, and the selectivity obtained was in the same range relative to those observed with the Al- and Sn-chloride-containing ionic liquids. 

Also, Marquie and co-workers have conducted Friedel-Crafts reactions on a large laboratory scale via a continuous flow process126. They reported the acylation of aromatic ethers and sulphonylation of mesitylene, isolating up to 300 g and 250 g of product, respectively (Schemes 9.13 and 9.14). 

In the Sc(0Tf)3-LiC104-system, wider substrate scope was observed as is shown in Table 8. Each acylation reaction in the Table gave a single acylation product and formation of other isomers was not observed. Acetylation of anisole (1) resulted in excellent yield of the product (entry 1). Mesitylene (3) and xylenes were transformed to 2,4,6-trimethylacetophenone and dimethylacetophenones, respectively, in moderate yields (entries 2-5). It is noteworthy that toluene was acylated by the Sc(0Tf)3-LiC104 system to give 4-methylacetophenone in 48 % yield (entry 6) but the acylation did not proceed in the absence of LiC104. Furthermore, recovery and reuse of the RE(0Tf)3-LiC104 system were performed successfully. As shown in Table 9, the yields of 6 in the second and third uses of the catalyst system were almost the same as that in the first use. 

Acylation, of amines with f-butyl azidoformate, 44, 17 of enamines by add halides, 43, 34 of ethyl acetoacetate by y-carbeth-oxybutyryl chloride, 42, 41 of mesitylene with oxalyl chloride, 44, 69... 

Thus, nitro compounds with a great number substituents, for example trinitro-mesitylene, do not give any colour reactions. Compounds with nitro groups located in the 2,4-positions, produce colours that depend to a considerable extent on the substituent in position 1. The presence of the OH or NH2 group interferes with the colour reaction. The situation remains unchanged after both of the groups have been acylated, while alkylation of a phenol restores the ability to produce colour,... 

Acylated or mesylated aldehyde adducts 301 react with enol silyl ethers 302 to provide products 303, after a phenylsulfanyl migration reaction. Oxidation of compounds 303 with MCPBA followed by heating under mesitylene reflux and acidic hydrolysis afforded 1,3-diketones 304, whereas treatment with potassium fert-butoxide followed by acidic hydrolysis provided 1,4-diketones 305 (Scheme 79)478. 

Catalytic acylation of electron-rich aromatics is achieved with a combination of InCls and silver perchlorate (Scheme 8.114) [157]. Acetic anhydride, acetyl chloride and isopropenyl acetate serve as satisfactory acyl donors. By using an InCl3-impreg-nated Si-MCM-41 catalyst at low concentration, acylation of aromatic compounds (benzene, toluene, p-xylene, mesitylene, anisole, naphthalene, methylnaphfhalene, and methoxynaphfhalene) by acyl chlorides (benzoyl chloride, phenylacetyl chloride, propionyl chloride, or butyryl chloride) can be accomplished rapidly (3 h) at 80 °C in high yield, even in the presence of moisture in the aromatic substrate or solvent (dichloroethane) (Scheme 8.115) [158], In(OTf) j is an efficient catalyst in the sulfonylation of both activated and deactivated aromatic compounds (Scheme 8.116) [159]. 

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