Arenes from ketones

Oxidation of Other Arenes. Aromatic compounds with longer alkyl side chains can be converted to ketones or carboxylic acids. All the previously discussed reagents except Cr02Cl2 usually afford the selective formation of ketones from alkyl-substituted arenes. Oxidation with Cr02Cl2 usually gives a mixture of products. These include compounds oxidized in the P position presumably formed via an alkene intermediate or as a result of the rearrangement of an intermediate epoxide.110,705... 

Protonation of nitroalkenes. This strong acid diprotonates nitroalkenes, even nitroethylene, to give N,N-dihydroxyiminium carbenium ions, which react with arenes to give arylated oximes. This overall process provides a route to a-aryl methyl ketones from 2-nitropropene.1... 

A more complicated pH-rate profile is also observed for the hydrolysis reactions of benzo[a]pyrene diol epoxide epoxide 80, and is shown in Fig. 5.102 This profile shows Regions A-D that are similar to those for reaction of precocene I oxide 76 (Fig. 4), except that Region B reaches a full plateau that extends from pH 5 to 9 in water. The interpretation of this pH-rate profile is essentially the same as the interpretation of the profile for hydrolysis of precocene I oxide (Fig. 4). The pH-independent reaction of 80 in Region B (discussed in detail in Section Benzylic epoxides and arene oxides ) yields 60% tetrols in a stepwise mechanism involving a carbocation intermediate and 40% ketone from a completely separate pathway (Scheme 31). The negative inflection of the profile at pH 10-11.5 indicates that hydroxide ion reacts as a base with the intermediate carbocation to reform diol epoxide 80 and thus slow the reaction rate. There is a corresponding increase in the yield of ketone 107 at pH >11. 

Starting from the readily available parent arenes, ketones 54a,b were prepared by standard Friedel-Crafts chemistry. Environment-friendly electrochemical carboxylation of these gave a-hydroxy acids 55a,b, from which acrylic acids 56a,b were easily obtained. Their reduction, catalyzed by the modified Noyori complex Ru(acac)2/BINAP, afforded in high yields the (. -enantiomers of acids 22 and 57 having 98% and 96% e.e., respectively. Improvements of both processes have been reported [64,65],... 

SYNTHESIS OF KETONES 16.5A Ketones from Alkenes, Arenes, and 2 Alcohols... 

Ketones from arenes by Friedel—Crafts acylations (discussed in Section 15.7). For example ... 

Tert. alcohols from ketones with subsequent aromatization hy dehydration Phenols and arenes from cyclohexenedione ring Selective formation of ketones from enolethers... 

Many aldehydes and ketones are made m the laboratory from alkenes alkynes arenes and alcohols by reactions that you already know about and are summarized m Table 17 1... 

ARENS VAN DORP Cinnamaldehyde Synthesis Synthesis ol cinnamaldehydes from aryl ketones... 

Noyori and coworkers reported well-defined ruthenium(II) catalyst systems of the type RuH( 76-arene)(NH2CHPhCHPhNTs) for the asymmetric transfer hydrogenation of ketones and imines [94]. These also act via an outer-sphere hydride transfer mechanism shown in Scheme 3.12. The hydride transfer from ruthenium and proton transfer from the amino group to the C=0 bond of a ketone or C=N bond of an imine produces the alcohol or amine product, respectively. The amido complex that is produced is unreactive to H2 (except at high pressures), but readily reacts with iPrOH or formate to regenerate the hydride catalyst. 

Scheme 3.12 Enantioselective hydrogenation of a ketone by transfer from iso-propanol catalyzed by the hydride complex RuH( 6-arene)(NH2CHPhCHPhNTs) and the amido complex Ru(r 6-arene)(NHCHPhCHPhNTs) [94].

We have found several examples in which adjacent cationic charge centers are shown to activate carboxonium electrophiles. A convenient method for studying this activation is through the use of the hydroxyalkylation reaction, a commercially important, acid-catalyzed condensation of aldehydes and ketones with arenes.10 It is used for example in the synthesis of bis-phenol A from acetone and phenol (eq 6). While protonated acetone is able to react with activated arenes like phenol, it is not capable of reacting with less nucleophilic... 

Rhodium and iridium nanoparhcles entrapped in aluminum oxyhydroxide nanofibers were shown by Park et al. to be suitable catalysts for the hydrogenation of arenes and ketones at room temperature, with hydrogen at ambient pressure [103]. Rhodium in aluminum oxyhydroxide [Rh/A10(0H)] and iridium in aluminum oxyhydroxide [Ir/A10(0H)], were simply prepared from readily available reagents such as RhCls and IrCls hydrates, 2-butanol and Al(O-sec-Bu) at 100°C. Substrates such as cyclopentanone, 2-heptanone, ethyl pyruvate, acetone and 2,6-dimethyl-4-heptanone were reduced to the corresponding alcohols either in n-hexane at room temperature (maximum TOF 99 h" for ethyl pyruvate) or in solventless conditions at 75 °C using 4 atm of H2 (maximum TOF 660h" for acetone, 330 for 2-heptanone). 

In addition to the former example, Pandey et al. achieved efficient a-aryla-tion of ketones by the reaction of silyl enol ethers with arene radical cations generated by photoinduced electron transfer from 1,4-dicyanonaphthalene. Using this strategy various five-, six-, seven-, and eight-membered benzannulated compounds are accessible in yields in the range 60-70% [39],... 

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