Diaryl ketones, formation

The asymmetric formation of industrially useful diaryl methanols can be realized through either the addition of aryl nucleophiles to aromatic aldehydes or the reduction of diaryl ketones. The latter route is frequently the more desirable, as the starting materials are often inexpensive and readily available and nonselective background reactions are not as common. For good enantioselectivity, chemical catalysts of diaryl ketone reductions require large steric or electronic differentiation between the two aryl components of the substrate and, as a result, have substantially limited applicability. In contrast, recent work has shown commercially available ketoreductase enzymes to have excellent results with a much broader range of substrates in reactions that are very easy to operate (Figure 9.6). ... 

Elba reaction org chem The formation of anthracene derivatives by dehydration and cycllzation of diaryl ketone compounds which have a methyl group or methylene group heating to an elevated temperature is usually required. elbs re.ak shan ( ELDOR See electron electron double resonance. ( el,dor or e el de o ar ( electrical calorimeter analy chem Device to measure heat evolved (from fusion or vaporization, for example) measured quantities of heat are added electrically to the sample, and the temperature rise is noted. a lek tra kal kal a rlm ad ar)... 

Rate constants and Arrhenius parameters for the reaction of Et3Si radicals with various carbonyl compounds are available. Some data are collected in Table 5.2 [49]. The ease of addition of EtsSi radicals was found to decrease in the order 1,4-benzoquinone > cyclic diaryl ketones, benzaldehyde, benzil, perfluoro propionic anhydride > benzophenone alkyl aryl ketone, alkyl aldehyde > oxalate > benzoate, trifluoroacetate, anhydride > cyclic dialkyl ketone > acyclic dialkyl ketone > formate > acetate [49,50]. This order of reactivity was rationalized in terms of bond energy differences, stabilization of the radical formed, polar effects, and steric factors. Thus, a phenyl or acyl group adjacent to the carbonyl will stabilize the radical adduct whereas a perfluoroalkyl or acyloxy group next to the carbonyl moiety will enhance the contribution given by the canonical structure with a charge separation to the transition state (Equation 5.24). 

This type of cyclobutanone annelation is feasible with various dibromocyclopropanes. When diaryl ketones are used as electrophiles, the oxaspiropentane-cyclobutanone rearrangement occurs spontaneously, so that the cyclobutanone is obtained directly (equation 63)"° . When 1-bromo-l-lithiocyclopropanes are allowed to react with aldehydes, the formation of cyclopropyl ketones results" . 

Diaryl ketones do not undergo photodissociation in the same way as alkyl ketones, probably because cleavage to phenyl and other aryl radicals is unfavorable (Table 4-6). Nevertheless, aromatic ketones are photochemically reactive in the presence of compounds that can donate a hydrogen atom, with the result that the carbonyl group is reduced. Indeed, one of the classic photochemical reactions of organic chemistry is the formation of 1,1,2,2-tetraphenyl-1,2-ethanediol (3, benzopinacol) by the action of light on a solution of diphenyl-methanone (2, benzophenone) in isopropyl alcohol. The yield is quantitative. 

Because the iron-catalyzed formation of diaryl ketones oftengives low yields, Knochel s group tackled this problem by introducing aroyl cyanides as alternative acylation agents [61]. These types of compounds are more powerful in acylation... 

Photoinitiators are generally aryl alkyl ketones or diaryl ketones (Table 2.19). For aryl alkyl ketones two free radicals are produced by homolytic scission of a C-C bond (Eq. (2.96)). Diaryl ketones are usually mixed with a tertiary amine the mechanism of production of free radicals involves H abstraction from the tertiary amine by the excited state PI, via a charge-transfer stabilized exciplex (Eq. (2.97)). The a-amino alkyl radical formed is very reactive and is in fact the true initiator because the cetyl radical disappears rapidly through a coupling reaction (formation of pinacol). 

The addition of hydrogen cyanide to carbonyl compounds gives a-hydroxy cyanides (cyanohydrin synthesis). The reaction is reversible, and the extent of the cyanohydrin formation depends upon the structure of the Carbonyl compound. The equilibrium highly favors the formation of aliphatic and alicyclic cyanohydrins however, aryl alkyl ketones react to a lesser extent, and diaryl ketones, not at all. The reaction may be accomplished by mixing the carbonyl compound with liquid hydrogen cyanide in the presence of a basic catalyst. The equilibrium... 

Early work by Papa et al. indicated that reduction of carbonyl compounds with Raney nickel in alkaline solution gave the corresponding hydrocarbon or alcohol products, and formation of the hydrocarbon was only feasible in the case of aromatic carbonyl compounds at 80-90 C. Mitchell et al. reported an improved method under neutral conditions using W-7 Raney nickel in 50% aqueous ethanol, aryl aldehydes, alkyl aryl and diaryl ketones can be reduced to the methylene products in high yields. Aromatic substituents such as nitro, cyano and halogen also suffer reduction under these conditions. 

Elbs reaction. Formation of anthracenes by intramolecular condensation of diaryl ketones containing a methyl or methylene substituent adjacent to the carbonyl group. 

Electrophilic substitution of phenones. The facile formation of C,0-dilithiated diarylmethanols from diaryl ketones and LN, coupled with subsequent reaction with various electrophiles, " solves the compatibility problem of the conventional addition reaction with functional nucleophiles to prepare diaryl r-carbinols. 

In particular, Russell and co-workers (37) have made extensive ESR studies on electron transfer from carbanions and nitranions to various acceptors including azobenzenes, diaryl ketones, and nitroaromatics. Some one-electron transfer processes have been investigated using a combination of electrochemical and ESR techniques (26). In these experiments, radical anions were produced electrochemically and introduced into a mixing chamber containing an aromatic electron acceptor. Electron transfer was indicated by the formation of the ESR spectrum of the resultant radical anion. It was verified that the direction of transfer between two reactants could be predicted from E0f values derived from polarographic data. 

Synthesis of anti-malarial reagent enpiroline (17) involved the formation of the pyridine skeleton 206 via the Krdhnke reaction of aroyl acrylic acid 204, acyl pyridinium salt 205, and ammonia acetate. Condensation of the carboxyl group in 206 with 2-lithiopyridine afforded the diaryl ketone 207. The relative higher basicity of the terminal pyridinyl ring allowed selective reduction of this ring via hydrogenation in the presence of an acid and simultaneously reduction of the ketone to the alcohol. The desired isomer was then obtained by fractional crystallization to afford 17. ... 

Additionally, the Hiyama coupling is called the palladium-catalyzed C-C bond formation between aryl, alkenyl, or alkyl halides with organosilanes. Among all the publications concerning Hiyama reactions, only a few described carbonylative Hiyama-type reactions. The first example was published in 1989 by Hiyama himself [83, 84]. Here, diaryl ketones were produced in good yields via the... 

There has been a review of palladium-catalysed carbonylative coupling reactions of aryl halides with carbon nucleophiles in the presence of carbon monoxide. It has been shown that rhodium is an efficient catalyst for the homocoupling reaction of arylzinc compounds in the presence of 1 atm of carbon monoxide to give diaryl ketones. Under similar conditions, palladium and nickel catalysts yield biaryls. The beneficial catalysis by rhodium is likely to derive from the ease of migration of the aryl ligand to carbon monoxide in the rhodium(III) intermediate. A rhodium catalyst has also been used in the formation of indole-3-carboxylates by reaction of indoles with alcohols in the presence of carbon monoxide. The catalytic cycle. Scheme 5, is likely to involve metallation of the indole at the 3-position, followed... 

As alluded (vide supra), some confusion may arise with respect to this named reaction as there is reference in the literature to an alternative reaction with the same name. The Bradsher reaction forms aromatic rings but via an acid-catalyzed Friedel-Crafts-like process. Thus diaryl-methanes having a carbonyl group in the ortho position can undergo a cyclodehydration reaction to generate the corresponding anthracene derivatives. In this respect, the Bradsher reaction is related to the Elbs reaction, which involves the pyrolytic cyclization of diaryl ketones 6 having an ortho methyl or methylene substituent for the formation of polycyclic aromatics 7. 

Hurd and Azorlosa performed deuterium labelling experiments of two different substrates 10 and 15. They subjected these two deuterated o-methylated-diaryl ketones to Elbs conditions and monitored where the deuterium went. Subsequent oxidation of the product mixture was used to determine the relative amount of %d vs. 9d formation. The fact that more Sd isomer was formed than 9d isomer is consistent with deuterium isotope effects. The authors foimd that < 1% of deuterium remained in the water derived from the reaction. The authors suggested that the low percentage of deuterium in the products was due to subsequent by-product formation. These experiments support a transfer of the aromatic H(D) (hydride transfer... 

Diaryl-a-diketones were obtained in the carbonylation of diaryliodonium salts catalyzed by Pd(OAc)2 in the presence of zincJ In addition to diketones, formation of diaryl ketones, biaryls, and aryl iodides was also found. A synthetic method to yield a-diketones has been developed by carbonylative coupling between diorganozincs and acid halides promoted by palladium complexes (Eq. 26). A diacylpalladium intermediate was proposed in the course of formation of a-diketone. 

The Pd-catalyzed formation of symmetrical diaryl ketones from arylmercuric salts was first reported by R. F. Heck. The reaction of phenylmercuric chloride with carbon monoxide... 

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