Aryl alkyl ketones irradiation

The dimerization of ketones to 1,2-diols can also be accomplished photochemi-cally indeed, this is one of the most common photochemical reactions. The substrate, which is usually a diaryl or aryl alkyl ketone (though a few aromatic aldehydes and dialkyl ketones have been dimerized), is irradiated with UV light in the presence of a hydrogen donor such as isopropyl alcohol, toluene, or an amine. In the case of benzophenone, irradiated in the presence of 2-propanol, the ketone molecule initially undergoes n — k excitation, and the singlet species thus formed crosses to the T, state with a very high efficiency. 

It is noticeable from the data in Table 1, that the number of examples of reactions involving the enolates of aryl alkyl ketones is limited. Bromo- and iodo-benzene were reported not to react with the enolate of acetophenone112 but the reaction with iodobenzene under more intense and longer irradiation was reported to give a 67% yield of phenacylbenzene.45 Sufficient examples of the ot-arylation of the enolates of aryl (and heteroaryl) alkyl ketones have been cited to indicate that these reactions are worth further investigation. 

Table II. Product Distribution Upon and in Cyclodextrins Irradiation of Aryl Alkyl Ketones in Organic Solvents ...

Me R = Br, R = H) by various donors in viscous soJventa are decreased by a factor of <2 in a 0.34 T magnetic field and pressure is reported to accelerate the photoreduction of p-benzoquinone in SOS and CTAB micelles in Aerosol OT reversed micelles, the reaction is retarded.The yield of anthraquinone-2-sulphonate radical anion (AQS) generated by irradiation of AQS in aqueous acetonitrile containing propan-2-oJ has been found to depend on the water concentration and to follow Perrin s equation.Complexation of aryl alkyl ketones with /3-cyclodextrin leads to changes in the ratio of the products of elimination and cyclisation which result from reaction of the... 

Amino-3-cyano-thiophenes or 2-amino-thiophene-3-esters result from this route, generally conducted as a one-pot process, involving a ketone that has an a-methylene, ethyl cyanoacetate or malononitrile, sulfur, and morpholine. Various improvements to the original procedure include using microwave irradiation on solid snpport, or with potassium fluoride on alumina as the base, or solvent-free,and using morpho-lininm acetate in excess morpholine for aryl alkyl ketones. 

Aryl alkyl ketone 4.5 A solution of ester 3 (500 mg 2 mmol) in hexane (450 mL) was irradiated for 6 h at 20°C with a 125W medium pressure lamp. The solvent was removed in vacuum and the residue chromatographed to give 360 mg of 4 (72%). 

Numerous useful organic transformations are known to be accelerated by US irradiation [51]. Compared to traditional methods, US-promoted methodologies are of more convenience and share many common features with other green chemical techniques [52]. An US-enhanced synthesis of 1,5-benzodiazepines (Scheme 12) catalyzed by p-toluenesulfonic acid (p-TSA) has been reported [53]. A variety of catalysts such as silica, Amberlyst 15, Dowef, K-10, ZnCl2, and so on were screened, but p-TSA was foxmd to be the best in terms of yield. The scope and limitation of the method was studied and it was foxmd that the reaction was unsuccessful with aryl alkyl ketones, a,(3-unsaturated ketones, and cyclic ketones. 

Moghaddam and Ghaffarzadeh (2001) have successfully transformed aldehydes and aryl alkyl ketones to thioamides with the same number of carbon atoms via Willgerodt-Kindler reaction under microwave irradiation in solvent-free conditions. 

The chiral auxiliary method yields exceptionally high de values even during intramolecular hydrogen abstraction reactions of carbonyl systems. A single isomer of highly substituted cyclopentanols was obtained when the chiraUy modified aryl alkyl ketones 27 shown in Scheme 26 were irradiated. ... 

For related reasons, and because their excited-state energies are lower than for dialkyl ketones, diaryl ketones and simple alkyl aryl ketones do not fragment on irradiation in solution, even at higher temperatures. This leads to a photostability that is one factor contributing to the successful employment of ketones such as benzophe-none tPh-CO) or acetophenone (PhCOMe) as triplet sensitizers. a-Cleavage for ketones in solution at room temperature is promoted if structural factors cause the bond adjacent to the carbonyl group to be somewhat weaker than normal. Hence t-alkyl ketones give decar-borylation products readily (4.5), as do benzyl ketones (4.6 and benzoin derivatives (4.7). 

Copolymers. The copolsmers were prepared by emulsion polymerization in a "pop bottle" polymerizer at 80° C using sodium aryl alkyl sulphonate (Ultrawet K) as emulsifier and ammonium persulphate as catalyst. The polymerizations were carried to greater than 95% conversion (4-8 hr) and the feed concentrations of the vinyl ketones were taken as their concentrations in the polymer. Copolymers containing 1% and 5% by weight of vinyl ketones were prepared. The cqsolymers were not homogeneous in ketone concentration since the reactivity ratios indicated that the vinyl ketones would be used ip before the end of the polymerizations. Thin films were prepared for irradiation by compression molding in a Carver Press at 150° C at 20,000 psi. The films were usually 0.22 mm thick. 

Aromatic ketones 569, benzylic alcohols 570 and 571 as well as alkyl aryl ethers 572 reacted with lithium under ultrasonic irradiation in the presence of catalytic amounts of DTBB (2%) in THF to give, after alkylation with an alkyl iodide at 0°C and final... 

Recently, however, examples of intramolecular triplet sensitization have been described. Alkyl aryl ketones with pendant azido groups in the alkyl moiety were irradiated into the benzoyl chromophore. The excited alkylphenyl ketones undergo intersystem crossing to their triplet states within picoseconds and they can then transfer their triplet energy to the nearby alkyl azido group. This process... 

Systems in which carbon-carbon bond cleavage in an aryl substituent leads to products In which the cleaved substituent Is bonded to the arene ring include the alkylated dibenzyl ketones (234). 51 Ramamurthy has compared the photochemistry of these compounds when Irradiated In solution with that obtained when they are irradiated in the presence of 9-cyclodextrin. In the absence of... 

The steroidal dienone (170) can be induced to undergo the relatively unusual reorganization to the 2-hydroxy-4-methylandrosta-l,3,5-triene (171), by irradiation in refluxing acetic acid although only 48% of the acetate (171) was isolated, the related 17-ketone (36%) was also formed. The p-dienones (172) and (173) are restructured on irradiation in cyclohexane with net relocation of methyl and t-butyl groups to afford the phenols (174) and (175) in 55% and 73% yield, respectively. A photo-induced aryl shift in the benzylisoquinoline dienone (176) was employed to prepare the aporphine (177 44%) en route to ( )-boldine. The p-dienones (178 X = Cl, X = Ns) aromatize on irradiation to yield the alkylated p-hydroxybenzoates (179 e.g. X = Ns, 57%) as well as minor quantities, of their isomers (180). Mechanistic aspects of these reactions are discussed in the literature cited. 

Several examples have appeared of diversion of the normal photochemistry of ortho-alkyl aromatic ketones due to apparent interception of the intermediate biradical by an unsaturated group present elsewhere in the molecule.Thus the vinyl aryl ketones (376) are converted to (377) in reasonable yields upon irradiation with ultra-violet light,while irradiation of the ortho-alkynyl acetophenone (378) in methanol yields diastereomers of (379)The latter reaction is thought to proceed by coupling of the initially formed ketyl radical onto the alkyne to give a carbene (380). The photochemistry of the jS-diketone (381) gives a mixture of the benzocyclobutenol (382) and the tetralone (383), and the proportions depend on the identity of the R-substituent in (381). The formation of (383) can be rationalised in terms of interception of the ketyl radical in the initially formed 1,4-biradical by the remote carbonyl group. 

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