Friedel-Crafts acylation synthetic applications

The synthetic importance of the Houben-Hoesch reaction is even more limited by the fact that aryl ketones are also available by application of the Friedel-Crafts acylation reaction. 

Stannic chloride is also used widely as a catalyst in Friedel-Crafts acylation, alkylation and cyclization reactions, esterifications, halogenations, and curing and other polymerization reactions. Minor uses are as a stabilizer for colors in soap (19), as a mordant in the dyeing of silks, in the manufacture of blueprint and other sensitized paper, and as an antistatic agent for synthetic fibers (see Dyes, application AND EVALUATION Antistatic agents). 

Gore, P. H. The Friedel-Crafts acylation reaction and its application to polycyclic aromatic hydrocarbons. Chem. Rev. 1955, 55, 229-281. Eyiey, S. C., Rainey, D. K. Aldehydes and ketones. General and Synthetic Methods 1981,4, 26-86. 

The Fries rearrangement of phenyl- and 1-naphthyl esters can be efficiently performed in the presence of hafnium triflate. The method is based on the one previously described for the Friedel-Crafts acylation of arenes with acyl chlorides. The reaction occurs in toluene-nitromethane mixtures at 100°C for 6 h. Several examples of this Fries isomerization with synthetic application are reported in Table 5.5. In all cases, complete regioselectivity is obtained, and 2-acylated phenol or naphthol derivatives are isolated in good yields. 

Synthetic Applications of Friedel-Crafts Acylations The Clemmensen and Wolff-Kishner Reductions 683... 

In its reactions, coordinated cyclobutadiene exhibits aromatic character, undergoing electrophilic substitution, e.g. Friedel-Crafts acylation. A synthetic application of (ri" -C4H4)Fe(CO)3 in organic chemistry is as a stable source of cyclobutadiene. Oxidation of the complex releases the ligand, making it available for reaction with, for example, alkynes as in scheme 24.135. 

It is well known (March, 1977) that an important synthetic application of Friedel Crafts alkylation and acylation is to effect ring closure. These reactions are most successful when 6-membered rings are formed, but 5- and 7-membered rings can be sythesised as well, although less readily. Quantitative data are not available, but the indication is strong that formation of... 

Ionic liquids can be used as replacements for many volatile conventional solvents in chemical processes see Table A-14 in the Appendix. Because of their extraordinary properties, room temperature ionic liquids have already found application as solvents for many synthetic and catalytic reactions, for example nucleophilic substitution reactions [899], Diels-Alder cycloaddition reactions [900, 901], Friedel-Crafts alkylation and acylation reactions [902, 903], as well as palladium-catalyzed Heck vinylations of haloarenes [904]. They are also solvents of choice for homogeneous transition metal complex catalyzed hydrogenation, isomerization, and hydroformylation [905], as well as dimerization and oligomerization reactions of alkenes [906, 907]. The ions of liquid salts are often poorly coordinating, which prevents deactivation of the catalysts. 

Influence of the Catalyst. Several different types of aromatic reactions are catalyzed by Lewis acids, including alkylation, polymerization, isomerization, acylation, and halogenation. The dependence of these reactions on various Lewis acids is shown in Table 12.11. This table shows a few common Lewis acids and the type of reaction(s) for which each is best suited. The relative strength of Lewis acids was discussed in Section 2.3. Olah gives a comprehensive list of Lewis acid catalysts, and includes several typical synthetic applications. Metal alkyl catalysts are also effective catalysts, but the aromatic substrate is usually converted to a mono-, di-, or trialkyl derivative. Both metal halides and their alkyl derivatives are effective Friedel-Crafts catalysts, as shown in Table 12.11,m as are common inorganic and organic acids. Triflate derivatives are trifluorosulfonate ester (—S02CF3 OTf) can be prepared with various metal counterions. Triflates are very effective catalyst in Friedel Crafts reactions. Some of the more common catalysts are B(OTf)3, Al(OTf)3, and Ga(OTf)3.ll3... 

Synthetic applications D. Villemin, B. Labiad, Synth. Commun. 22, 3181 (1992) S. Nakanishi etal., ibid. 28,1967 (1998). Cf. Friedel-Crafts Reaction Nencki Reaction Nenitzescu Reductive Acylation. 

Compared to the relatively young history of the pure metal, aluminium compounds have been known for ages from the above-cited alum class to the more exclusive transition metal-doped aluminium oxides like ruby and sapphire (corundum varieties with chromium for the former and titanium and iron impurities for the latter) or aluminosilicate-like emeralds (a beryl type with chromium and vanadium impurities). However, to the synthetic chemist, aluminium chloride, is de facto one of the first jewels of the aluminium family. Aluminium trichloride (together with titanium tetrachloride, tin tetrachloride and boron trifluoride) is an exemplary Lewis acid that finds many applications in organic synthesis It is extensively used for instance in Friedel-Crafts alkylations and acylations, in Diels-Alder-type cycloadditions and polymerisation reactions. Its involvement in a wide range of reactions has been documented in many reviews and book chapters. ... 

From the same element group Ga(OTf)3 demonstrated its advantages in several synthetic applications over similar catalysts [1]. Very low catalyst loadings were enough to drive various acid-catalyzed reactions including Friedel-Crafts alkylation, hydroxyalkylation, and acylation... 

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