Acyl nitrates, with arenes

It is generally admitted that skeletal transformations of hydrocarbons are catalyzed by protonic sites only. Indeed good correlations were obtained between the concentration of Bronsted acid sites and the rate of various reactions, e g. cumene dealkylation, xylene isomerization, toluene and ethylbenzene disproportionation and n-hexane cracking10 12 On the other hand, it was never demonstrated that isolated Lewis acid sites could be active for these reactions. However, it is well known that Lewis acid sites located in the vicinity of protonic sites can increase the strength (hence the activity) of these latter sites, this effect being comparable to the one observed in the formation of superacid solutions. Protonic sites are also active for non skeletal transformations of hydrocarbons e g. cis trans and double bond shift isomerization of alkenes and for many transformations of functional compounds e.g. rearrangement of functionalized saturated systems, of arenes, electrophilic substitution of arenes and heteroarenes (alkylation, acylation, nitration, etc ), hydration and dehydration etc. However, many of these transformations are more complex with simultaneously reactions on the acid and on the base sites of the solid... 

Nitration. When immobilized, the acyl nitrates effect mononitration of arenes with good regioselectivity (6 examples, 86-100%). 

The high reactivity of ferrocene toward electrophilic substitution was described earlier. Similar reactions of arene Ti-complexes result in the cleavage of the complexed bonds. For example, Friedel-Crafts acylation, metalation with butyllithium, mercuration, or nitration of ditoluenechromium, which is more soluble in organic solvents than the slightly soluble dibenzenechro-mium, failed to give any substitution products. 

In arene complexes, there is a charge transfer from the ring to the metal. Therefore, coordinated arenes undergo electrophilic substitutions with greater difficulty than free arenes. Owing to the sensitivity to acids and easy oxidation of bisarene complexes, it has not been possible to perform sulfonation, nitration, and mercuration. However, the acylation reaction of chromium derivatives [Cr(arene)(CO)3] can be carried out ... 

Methylseleno esters are readily available in excellent yields by the reaction of Dimethylaluminum Methylselenolate with O-alkyl esters. These selenoesters will acylate reactive arenes (eq 69) and heterocyclic compounds (eq 70) when activated by CuOTf, a selenophilic Lewis acid. Of the potential activating metal salts tested, (CuOTf)2 QHe is uniquely effective. Mer-cury(ll) or copper(l) trifluoroacetates that are partially organic-soluble, as well as the corresponding chlorides, silver nitrate, and... 

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