Carbonyls, aromatic

Polycyclic Aromatic Carbonyl Dyes. StmcturaHy, these dyes contain one or more carbonyl groups linked by a quinonoid system. They tend to be relatively large molecules built up from smaller units, typically anthraquinones. Since they are appHed to the substrate (usually cellulose) by a vatting process, the polycycHc aromatic carbonyl dyes are often called the anthraquinonoid vat dyes. 

Although the colors of the polycycHc aromatic carbonyl dyes cover the entire shade gamut, only the blue dyes and the tertiary shade dyes, namely, browns, greens, and blacks, are important commercially. Typical dyes are the blue indanthrone [81-77-6] (40), the brown Cl Vat Brown 3 [131-92-0] (Cl 69012), (41), the black Cl Vat Black 27 [2379-81-9] (42), and the green Cl Vat Green 1 [128-58-5] (Cl 59825) (43), probably the most famous of all the polycycHc aromatic carbonyl dyes. 

Indigoid Dyes. Like the anthraquinone, ben2odifuranone, and polycycHc aromatic carbonyl dyes, the indigoid dyes also contain carbonyl groups. They are also vat dyes. 

As discussed in Section 4.01.5.2, hydroxyl derivatives of azoles (e.g. 463, 465, 467) are tautomeric with either or both of (i) aromatic carbonyl forms (e.g. 464,468) (as in pyridones), and (ii) alternative non-aromatic carbonyl forms (e.g. 466, 469). In the hydroxy enolic form (e.g. 463, 465, 467) the reactivity of these compounds toward electrophilic reagents is greater than that of the parent heterocycles these are analogs of phenol. 

The 4- and 5-hydroxy-imidazoles, -oxazoles and -thiazoles (499, 501) and 4-hydroxy-pyrazoles, -isoxazoles and -isothiazoles (503) cannot tautomerize to an aromatic carbonyl form. However, tautomerism similar to that which occurs in hydroxy-furans, -thiophenes and -pyrroles is possible (499 500 503 504 501 502), as well as a zwitterionic... 

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 ... 

Aldehydes and ketones are similar in their response to hydrogenation catalysis, and an ordering of catalyst activities usually applies to both functions. But the difference between aliphatic and aromatic carbonyls is marked, and preferred catalysts differ. In hydrogenation of aliphatic carbonyls, hydrogenolysis seldom occurs, unless special structural features are present, but with aryl carbonyls either reduction to the alcohol or loss of the hydroxy group can be achieved at will. 

A variety of catalysts including copper, nickel, cobalt, and the platinum metals group have been used successfully in carbonyl reduction. Palladium, an excellent catalyst for hydrogenation of aromatic carbonyls is relatively ineffective for aliphatic carbonyls this latter group has a low strength of adsorption on palladium relative to other metals (72,91). Nonetheless, palladium can be used very well with aliphatic carbonyls with sufficient patience, as illustrated by the difficult-to-reduce vinylogous amide I to 2 (9). 

Hydrogenolysis of aliphatic carbonyls usually does not occur readily unless certain types of structures prevail (78), but hydrogenolysis of an aromatic carbonyl will occur easily, mostly via an intermediate benzyl alcohol. 

Hydrogenolysis of aromatic carbonyls occurs mainly by conversion to the benzyl alcohol and its subsequent loss. If hydrogenolysis is desired, the usual catalyst is palladium 38). Hydrogenolysis is facilitated by polar solvent and by acid (55). For instance, hydrogenation of 3,3-dicarbethoxy-5,8-dimethoxy-l-tetralone (5) over 5% Pd-on-C gave 6 quantitatively 54) when hydrogen absorption ceased spontaneously. 

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

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 ... 

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 reaction is stereospecific for at least some aliphatic ketones but not for aromatic carbonyls.197 This result suggests that the reactive excited state is a singlet for aliphatics and a triplets for aromatics. With aromatic ketones, the regioselectivity of addition can usually be predicted on the basis of formation of the more stable of the two possible diradical intermediates obtained by bond formation between oxygen and the alkene.198... 

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... 

With aromatic carbonyls, oxetane formation appears to arise from the carbonyl triplet state, as evidenced by quenching studies. For example, benzaldehyde irradiated in the presence of cyclohexene yields products indicative of hydrogen abstraction reactions and an oxetane ... 

Table 4.10. Reactivity of Various Aromatic Carbonyls toward Oxetane Formation and Photoreduction Compared to the Nature of the Lowest TripletiB3,9 Bm...

The triplet lifetimes of various aromatic, carbonyl, and heterocyclic compounds are listed in Tables 5.8A-5.8C. 

We have also examined the behavior of copolymers of o-tolyl vinyl ketone and methyl vinyl ketone (CoMT). In this case the light is absorbed exclusively at the aromatic carbonyl chromophore and the reaction proceeds from this site, while the methyl vinyl ketone moieties provide a relatively constant environment but prevent energy migration along the chain. The values of Tg and Tip in benzene have been included in Table II. These copolymers axe also soluble in some polar solvents for example, we have used a mixture of acetonitrile acetone methanol (30 30 Uo, referred to as AAM). This mixture is also a good solvent for the electron acceptor paraquat (PQ++) which has been shown to be good biradical trap in a number of other systems (9.). 

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

Termination is principally via radical coupling forming hexabutylditin, or to a lesser degree via the coupling of ketyl radicals. In the case of the mr ketones a different mechanism is proposed. The rate of abstraction of H from the tributyltinhydride by benzylic radicals is slower than the corresponding abstraction by alkyl radicals. Since the rate at which the tributyltin radical will add to aromatic carbonyls is similar to the addition rate to aliphatic carbonyls, the dominant radical species for the tttt systems is the ketyl radical. The primary termination process involves the coupling of the predominant radical species resulting in pinacol formation. 

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. 

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