Friedel-Crafts alkylation, and

Nitration in sulphuric acid is a reaction for which the nature and concentrations of the electrophile, the nitronium ion, are well established. In these solutions compounds reacting one or two orders of magnitude faster than benzene do so at the rate of encounter of the aromatic molecules and the nitronium ion ( 2.5). If there were a connection between selectivity and reactivity in electrophilic aromatic substitutions, then electrophiles such as those operating in mercuration and Friedel-Crafts alkylation should be subject to control by encounter at a lower threshold of substrate reactivity than in nitration this does not appear to occur. 

Other typical electrophilic aromatic substitution reactions—nitration (second entry) sul fonation (fourth entry) and Friedel-Crafts alkylation and acylation (fifth and sixth entnes)—take place readily and are synthetically useful Phenols also undergo elec trophilic substitution reactions that are limited to only the most active aromatic com pounds these include mtrosation (third entry) and coupling with diazomum salts (sev enth entry)... 

Other methods for the regioselective SN2-opening of vinyloxiranes include intramolecular enolate addition for formation of cyclohexane systems [135, 136] and Friedel-Crafts alkylations [49, 137, 138]. 

The synthesis of alkylbenzenes may be classified under (a) the Wurtz-Fittig reaction (b) the reduction of aryl aldehydes and ketones and (c) and Friedel-Crafts alkylation reaction. 

As indicated from computational studies, the catalyst-activated iminium ion MM3-2 was expected to form with only the (E)-conformation to avoid nonbonding interactions between the substrate double bond and the gem-dimethyl substituents on the catalyst framework. In addition, the benzyl group of the imidazolidinone moiety should effectively shield the iminium-ion Si-face, leaving the Re-face exposed for enantioselective bond formation. The efficiency of chiral amine 1 in iminium catalysis was demonstrated by its successful application in several transformations such as enantioselective Diels-Alder reactions [6], nitrone additions [12], and Friedel-Crafts alkylations of pyrrole nucleophiles [13]. However, diminished reactivity was observed when indole and furan heteroaromatics where used for similar conjugate additions, causing the MacMillan group to embark upon studies to identify a more reactive and versatile amine catalyst. This led ultimately to the discovery of the second-generation imidazolidinone catalyst 3 (Fig. 3.1, bottom) [14],... 

Predict products and propose mechanisms for the common electrophilic aromatic substitutions halogenation, nitration, sulfonation, and Friedel-Crafts alkylation and acylation. Problems 17-44, 47, 48, 51, 59, G4, and 70... 

Solid acid catalysts are, in principle, applicable to a plethora of acid-promoted processes in organic synthesis [27-29]. These include various electrophilic aromatic substitutions, e.g. nitrations, and Friedel-Crafts alkylations and acylations, and numerous rearrangement reactions such as the Beckmann and Fries rearrangements. 

HPAs, however, is their solubility in polar solvents or reactants, such as water or ethanol, which severely limits their application as recyclable solid acid catalysts in the liquid phase. Nonetheless, they exhibit high thermal stability and have been applied in a variety of vapor phase processes for the production of petrochemicals, e.g. olefin hydration and reaction of acetic acid with ethylene [100, 101]. In order to overcome the problem of solubility in polar media, HPAs have been immobilized by occlusion in a silica matrix using the sol-gel technique [101]. For example, silica-occluded H3PW1204o was used as an insoluble solid acid catalyst in several liquid phase reactions such as ester hydrolysis, esterification, hydration and Friedel-Crafts alkylations [101]. HPAs have also been widely applied as catalysts in organic synthesis [102]. 

Pentacyclic derivatives 48 of the benzoazepine (-)-clavizepine were synthesised using three different methods for the formation of the azepine ring including radical, palladium and Friedel-Crafts alkylation and acylation, the most successful being the latter. <07JOC8804>. 

As we have already shown, the creation of novel carbon-carbon bonds usually results in the formation of functionalized derivatives (the Wurtz coupling and Friedel-Crafts alkylation are probably the only exceptions). That is why a set of special reductive methods was devised to remove residual functionality that is unwanted in the final structure. The well-known hydrogenation of alkenes and alkynes belongs to this group of non-isohypsic transformations. Several other pathways available for the reductive removal of various functions will briefly be considered below. 

The answer is found in a series of studies begun by Lars Melander (of the Nobel Institute of Chemistry, Stockholm) and extended by many other workers. A variety of aromatic compounds labeled w ith deuterium or tritium were subjected to nitration, bromination, and Friedel-Crafts alkylation. It was found that in these reactions deuterium or tritium is replaced at the same rate as protium there is no significant isotope effect. 

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