Acyl with electron donating substituents

In the RE(OTf)3-catalyzed Friedel-Crafts acylation, the acylation of aromatic compounds with electron-donating substituents, for example anisole and mesity-lene, proceeded smoothly whereas the reactivity of benzene, toluene, and xylenes was low under the same conditions. On the other hand, it was revealed that the catalyst activity of RE(OTf)3 was increased when combined with LiC104, and that the acceleration effect was strongly dependent on the amount of LiC104. 

It is known that, in acylation reactions in homogeneous [14,15] or heterogeneous [16] conditions, the rate determining step is the attack of the electrophilic species RCO+, previously formed in a fast step, on the aromatic ring. Electrophilicity of benzoyl cations X-Ar-CO+ increases with the presence of electron-withdrawing substituent, while it decreases with electron-donating substituents on the aromatic ring. 

Their yields are (1) higher in polar and lower in nonpolar solvents (2) increased by the presence of electron donating substituents in the phenolic nucleus and electron withdrawing substituents on the acyl moiety and (3) independent of the solvent viscosity. Their formation is possible even if the orf/io-position of the original aryl ester is substituted with — 1, + M substituents (e.g., chlorine, methoxy). They are extraordinarily stable to further photochemical reactions. 

The oxidation of indoles and pyrroles by Fe(III) ions is less predictable than other chemical oxidations. 2-Methyl- and 3-methyl-indoles, respectively, yield (187) and (188), and whilst pyrroles may form pyrrole black , the rate of oxidation of pyrrole and of 1-methylpyrrole appears to be relatively slow. C-Alkyl and electron-donating substituents enhance the formation of oligimers, e.g. (189) -> (190) and (191) -> (192), and although electron-withdrawing substituents reduce the susceptibility of the pyrrole ring to oxidation, acyl- and alkoxycarbonyl-pyrroles of the type (193) are readily oxidized to the thermochromic dimer (194), which is in equilibrium with the dimer (195) via the monomeric pyrrolyl radical (72BCJ3584). 

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