Aromatic carbonyl compound

Aromatic carbonyl compounds are protonated in strongly acidic media, like sulfuric and chlorosulfonic acid (Equation 69). As a consequence, the carbonyl group exerts a powerful electron-withdrawing effect on the attached aromatic 

More recent attempts to chlorosulfonate o-vanillin 215, vanillin 216 and 2,5-dimethoxybenzaldehyde with chlorosulfonic acid, under various conditions, were imsuccessful and the reactions only afforded charred products. In contrast, aromatic ketones of both the alkyl aryl and diaryl type have been successfully reacted with chlorosulfonic acid. -  

Many reviews have been written on the photochemistry of aromatic carbonyl 

Many reviews have been written on the photochemistry of aromatic carbonyl compounds269 and on the use of these compounds as photoinitiators.270 272 Primary radicals are generated by one of the following processes  

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The irradiation is usually carried out with light of the near UV region, in order to activate only ihc n n transition of the carbonyl function," thus generating excited carbonyl species. Depending on the substrate, it can be a singlet or triplet excited state. With aromatic carbonyl compounds, the reactive species are usually in a Ti-state, while with aliphatic carbonyl compounds the reactive species are in a Si-state. An excited carbonyl species reacts with a ground state alkene molecule to form an exciplex, from which in turn diradical species can be formed—e.g. 4 and 5 in the following example ... 

Hutchinson, J. and Ledwith, A. Photoinitiation of Vinyl Polymerization by Aromatic Carbonyl Compounds. Vol. 14, pp. 49 — 86. 

Highly enantioselective hydrosilylation of aliphatic and aromatic carbonyl compounds such as acetophenone, methyl phenethyl ketone 1813, or deuterobenz-aldehyde 1815 can be readily achieved with stericaUy hindered silanes such as o-tolyl2SiH2 or phenyl mesityl silane 1810 in the presence of the rhodium-ferrocene catalyst 1811 to give alcohols such as 1812, 1814, and 1816 in high chemical and optical yield [47] (Scheme 12.14). More recently, hydrosilylations of aldehydes... 

The palladium-catalyzed carbonylation of aryl halides in the presence of various nucleophiles is a convenient method for synthesizing various aromatic carbonyl compounds (e.g., acids, esters, amides, thioesters, aldehydes, and ketones). Aromatic acids bearing different aromatic fragments and having various substituents on the benzene ring have been prepared from aryl iodides at room temperature under 1 atm... 

Lamola AA, Sharp LJ (1966) Environmental effects on the excited states of o-hydroxy aromatic carbonyl compounds. J Phys Chem 70 2634—2638... 

More recently, we have been engaged in mechanistically related car-bonylations of aryl halides (Klaus et al. 2006). As demonstrated in Scheme 5, such reactions offer numerous possibilities for the selective synthesis of aromatic carbonyl compounds. 

Among the different aromatic carbonyl compounds, aldehydes are probably the most useful class of products, as the highly reactive aldehyde group can be easily employed in numerous C-C-, and C-N-coup-ling reactions, reductions as well as other transformations. 

The palladium-catalyzed arylations of aromatic carbonyl compounds such as ketones,67,67a amides (Equation (60)),68 and aldehydes69 with aryl halides and triflates give the multiple arylation products similarly. 

The ruthenium-, rhodium-, and palladium-catalyzed C-C bond formations involving C-H activation have been reviewed from the reaction types and mechanistic point of view.135-138 The activation of aromatic carbonyl compounds by transition metal catalyst undergoes ortho-alkylation through the carbometallation of unsaturated partner. This method offers an elegant way to activate C-H bond as a nucleophilic partner. The rhodium catalyst 112 has been used for the alkylation of benzophenone by vinyltrimethylsilane, affording the monoalkylated product 110 in 88% yield (Scheme 34). The formation of the dialkylated product is also observed in some cases. The ruthenium catalyst 113 has shown efficiency for such alkylation reactions, and n-methylacetophenone is transformed to the ortho-disubstituted acetophenone 111 in 97% yield without over-alkylation at the methyl substituent. 

Outline the basis of El-Sayed s rules and be able to use these to explain the differences in luminescence properties between aliphatic and aromatic carbonyl compounds. 

The fluorescence properties of aromatic carbonyl compounds are complex and often difficult to predict. 

Some aromatic carbonyl compounds have a low-lying n-n excited state and thus have a reasonable quantum yield (e.g. 0.12 for fluorenone in ethanol at 77 K and 0.01 at room temperature). However, if an n-n state lies only slightly higher in energy, the fluorescence quantum yield strongly depends on the polarity of the... 

Aldehydes and ketones can be hy-drodimerized to pinacols (Eq. 2) [34-37]. With aromatic carbonyl compounds, the yields and selectivities are mostly higher than with aliphatic ones. The reaction has been extended to imines (Eq. 2, X = NAr, N-Bn) [38-41] and to heterohydrodimerizations affording, for example, y-lactones (Eq. 3) [42-44]. 

Intermolecular coupling Many papers on hydrodimerization of aromatic carbonyl compounds have appeared indicating the importance of this reaction. The rac/meso ratio for the pinacolization of acetophenone in aqueous ethanol ranges between 0.9 and 1.4 in acidic medium and between 2.5 and 3.2 in basic medium. The diastereoselectivity is independent of the cathode material mercury, tin, or copper. Electrolysis conditions such as current density, potential, or current-controlled electrolysis also do not influence the diastereoselectivity. The same holds for propiophenone. For benzaldehyde, the rac/meso ratio is 1.1 to 1.2 in acidic as well as in basic media [283]. In the presence... 

Radical anion EGBs derived from aromatic carbonyl compounds are expected to be relatively weak bases but since the radical anions undergo dimerization, the more basic dimer dianions may be active as EGBs for substrates with pK values in the range 20 to 23. Aromatic carbonyl compounds have primarily been used as PBs in catalytic reactions in which the PB also functions as an electrophile (cf. Sect. 14.9.2). 

Another example is the electrocatalytic reaction between aromatic carbonyl compounds and dialkyl phosphonates. Here, rearrangement of the product anion leads to a phosphate as the product [136]. 

The oxygen-perturbed singlet-triplet spectra of aromatic carbonyl compounds were investigated by Warwick and Wells (Fig. 23). Transitions to states were enhanced by the perturbing agent while transitions to (n,7t ) states remained unaffected. It should be mentioned, however, that Evans also observed an oxygen-perturbed increase of the intensity of the Tnn So transitions in pyrazine and acridine. 

Warwick. D. A., Wells, C. H. J. Perturbation of singlet-triplet transitions in aromatic carbonyl compounds. Spectrochim. Acta 24A, 589 (1968). 

Figure 2. The correlation of plfBH Values of aromatic carbonyl compounds RCOX with carbonyl frequencies.

Tellurium powder/KOH is an efficient system for the pinacolization of aromatic carbonyl compounds. ... 

Scheme 54 Photoreaction of aromatic carbonyl compounds with p,p-dimethyl ketene silyl acetals.

Table 2 Formation Constants K), Fluorescence Maxima (Xmax), Fluorescence Lifetimes (x), the One-Electron Reduction Potentials (E°ed ) of the Singlet Excited States of Mg(C104)2, Sc(OTf)3 and MesSiOTf Complexes of Aromatic Carbonyl Compounds...

Determined from the spectral change of aromatic carbonyl compounds in the presence of metal ion salts. 

Trimethylsilyl triflate (McsSiOTf) acts as an even stronger Lewis acid than Sc(OTf)3 in the photoinduced electron-transfer reactions of AcrCO in dichloro-methane. In general, such enhancement of the redox reactivity of the Lewis acid complexes leads to the efficient C—C bond formation between organosilanes and aromatic carbonyl compounds via the Lewis-acid-catalyzed photoinduced electron transfer. Formation of the radical ion pair in photoinduced electron transfer from PhCHiSiMes to the (l-NA) -Mg(C104)2 complex (Scheme 11) and the AcrCO -Sc(OTf)3 complex (Scheme 12) was confirmed by the laser flash experiments [113]. 

Knowledge of the variation of electron transfer rate with electrode potential is important for the understanding of electrochemical reactions. The first experiments in this area were prompted by the observation that nitrobenzenes and aromatic carbonyl compounds are reduced in acid solution with little competition from the hydrogen evolution process. This is the case even though the electrode potential is more negative than the value calculated for the reversible evolution of hydrogen in the same solution. The kinetics of hydrogen evolution have been examined in detail. 

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