Arenes functionalized compounds

The corresponding catalytic version of this reaction was performed using either naphthalene- or biphenyl-supported polymers 594 or 595, respectively, which were prepared by cross-coupling copolymerization of 2-vinylnaphthalene or 4-vinylbiphenyl with vinyl-benzene and divinylbenzene promoted by AIBN in THF and polyvinyl alcohoP . These polymers have been used as catalysts (10%) in lithiation reactions involving either chlorinated functionalized compounds or dichlorinated materials in THF at —78°C and were re-used up to ten times without loss of activity, which is comparable to the use of the corresponding soluble arenes. 

Hydrocarbons contain only hydrogen and carbon. The hydrocarbon functional groups include alkanes, alkenes, alkynes, and arenes (aromatic compounds). Simple hydrocarbons have few medicinal applications, but are the feedstock of the petrochemical industry to produce plastics, dyes, solvents, detergents, and adhesives (to name just a few). Therefore, hydrocarbons are essential to the medical field. Additionally, all hydrocarbons are flammable and, therefore, find application as fuels. For example, gasoline is a mixture of hydrocarbons. 

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... 

Modern aspects of electrophilic aromatic substitution chemistry address the development of enantioselective variants of these direct (hetero)arene functionalization reactions. For example, enantiomerically enriched metal catalysts, as well as organocatalysts, allowed for the asymmetric addition reactions of (hetero)arenes onto (a,P-unsaturated) carbonyl compounds. Additionally, highly enantioselective arylations of carbonyl compounds were accomplished with organometallic reagents... 

This work represents a landmark in the area of stereoselective metal-free (i.e., aminocatalysis) alkylation of benzenes based on Michael-type condensation via covalent catalyst-substrate interaction [22]. Subsequently, asymmetric acid catalysis based on hydrogen bond catalyst-substrate recognitions has found elegant applications in 1,4-conjugated additions and direct condensation of arenes with carbonyl compounds. The following sections will be organized based on the reactivity exploited in the arene functionalization. 

Catalytic arylation via C-H functionalization has certainly become one of the most powerful methods of accessing key arene-containing compounds over the last 10 years. It has in fact, experienced an explosion in activity, and stfil without a doubt much more is yet to come. Metal-based catalysts, generally, based on Pd, Rh, and Ru, have generally led the way, with cheaper metals such as, Cu and Fe, making an impact. Organocat2dysts can also be used, but currently their application is less developed that their metal-based cousins. 

An amide was also successfully used as a directing group for the ortho-fluorination of arenes (Scheme 7.65) [107]. The investigation started by screening a range of functionalized compounds for activity in the fluorination reaction. Simple compounds such as benzoic... 

Oxidative cleavage of 280 by copper(ll) acetate generates a peroxy radical, which oxidizes the substrate to form an alcohol function and an oxy radical. Further reaction with the substrate affords again the corresponding alcohol in addition to a carbon radical. Thus, two equivalents of alcohol and only one equivalent of the carbon radical are formed. Since the reaction products originate from the carbon radical (see Fig. 112), the maximum yield could be 33%. The combined yields of 274 on one hand and 275-279 on the other hand are actually higher, hence further reduction of the alcohol must have occurred. It is very iikely that the copper(l) ion, which behaves as a moderately strong reductant (99), converts the alcohol, at least partially, to the reactive carbon radical. This mechanism explains the catalytic activity of copper(ll) acetate and resembles the reaction of arene diazonium compounds with copper(l) salts (100). 

The symmetric series provides functional cyclohexadienes, whereas the non-symmetric one serves to build deuterated and/or functional arenes and tentacled compounds. In both series, several oxidation states can be used as precursors and provide different types of activation. The complexes bearing a number of valence, electrons over 18 react primarily by electron-transfer (ET). The ability of the sandwich structure to stabilize several oxidation states [21] also allows us to use them as ET reagents in stoichiometric and catalytic ET processes [18, 21, 22]. The last well-developed type of reactions is the nucleophilic substitution of one or two chlorine atoms in the FeCp+ complexes of mono- and o-dichlorobenzene. This chemistry is at least as rich as with the Cr(CO)3 activating group and more facile since FeCp+ activator is stronger than Cr(CO) 3. 

An /n-geometry can be ensured by appropriate substitution of the building block which carries the acid-base functionality, for instance by using 2,6-disubstituted aromatic compounds like pyridines, 2,6-disubstituted benzoic acids or other 2,6-disubstituted phenyl derivatives (see Scheme 1). The use of 2,6-disubstituted arenes is sometimes called the 1,3-xylyl trick and assures an intra-annular orientation. 

The scopes outlined above limit the purpose of this chapter, which will not cover (1) the transition metal complexation by protonated or functionalized forms of calix[4]arenes (2) the metalation of calix[4]arenes using non-transition metals and (3) chemical curiosities derived from the metalation of calix[4]arenes (some recent reviews cover these areas very well).1 In addition, the authors have been particularly careful to report only those compounds which have a well-established synthesis and a full spectroscopic and structural characterization. 

---