Ketones, aryl reduction

Prochiral aryl and dialkyl ketones are enantioselectively reduced to the corresponding alcohols using whole-cell bioconversions, or an Ir1 amino sulfide catalyst prepared in situ.695 Comparative studies show that the biocatalytic approach is the more suitable for enantioselective reduction of chloro-substituted ketones, whereas reduction of a,/ -unsaturated compounds is better achieved using the Ir1 catalyst. An important step in the total synthesis of brevetoxin B involves hydrogenation of an ester using [Ir(cod)(py) P(cy)3 ]PF6.696... 

Catalytic processes based on the use of electrogenerated nickel(O) bipyridine complexes have been a prominent theme in the laboratories of Nedelec, Perichon, and Troupel some of the more recent work has involved the following (1) cross-coupling of aryl halides with ethyl chloroacetate [143], with activated olefins [144], and with activated alkyl halides [145], (2) coupling of organic halides with carbon monoxide to form ketones [146], (3) coupling of a-chloroketones with aryl halides to give O -arylated ketones [147], and (4) formation of ketones via reduction of a mixture of a benzyl or alkyl halide with a metal carbonyl [148]. 

The quaternary salts of ketals of 4-pyridyl alkyl and aryl ketones undergo reduction with sodium borohydride to give the expected 1,2,3,6-tetrahydropyridines.47" Reduction of an analogous ketal of a quaternary salt of a 3-pyridyl ketone led to rupture of the ketal ring.476... 

Selective reduction of aldehydes. In the absence of radical initiators, tributyltin hydride does not ordinarily reduce carbonyl groups. However, when slurried in cyclohexane with dried silica gel (activated by heating at 220° under reduced pressure), this hydride reduces aldehydes and ketones to alcohols in high yield. The rate of reduction is aldehydes > dialkyl ketones > aryl alkyl ketones > diaryl ketones. Thus it is possible to reduce aldehydes selectively. The function of Si02 apparently is that of a mild acid catalyst. 

Aryl vinyl ketones undergo reduction exhaustively to give arylpropanes in high yields. Anthraqui-none derivatives also react with EtjSiH/TFA to afford the corresponding hydrocarbons, while p-quinone was converted to hydroquinone in 98% yield. ... 

When aliphatic nitro compounds are used instead of aldehydes or ketones, no reduction occurs, and the reaction has been referred to as a Tollens reaction (see 16-43). However, the classical condensation of an aliphatic nitro compound with an aldehyde or ketone is usually called the Henry reaction or the Kamlet reaction, and is essentially a nitro aldol reaction. A variety of conditions have been reported, including the use of a silica catalyst, Mg—A1 hydrotalcite, a tetraalkylam-monium hydroxide,proazaphosphatranes, " or an ionic liquid.A solvent free Henry reaction was reported in which a nitroalkane and an aldehyde were reacted on KOH powder. Potassium phosphate has been used with nitromethane and aryl aldehydes. The Henry reaction has been done using ZnEt2 and 20%... 

For aryl ketones the reduction must be stopped after absorption of 1 mol of Hj because the carbonyl group in these compounds is easily reduced. Palladium catalysts should he used. When the double bond is substituted with an aryl group, reduction of the carbonyl becomes even easier. Palladium is more selective as shown in the reduction in high yields of 2-benzylidenecyclopentanone, 3, to 2-benzylcyclopentanone, 4 ... 

De-N-protectionJ A-Allyl and A-benzyl derivatives undergo dealkylation on heating with TiClj-Li in THF under argon. The application of this method to the deoxygenation of aryl ketones via reductive amination with aniline is too elaborate (taking three steps) to be of any synthetic significance. 

Tetraphenylethylene Glycol. This prcp iration illustnites the mild conditions under which aryl ketones may undergo bimolecular reduction to com-... 

The carbonylation of aryl iodides in the presence of alkyl iodides and Zn Cu couple affords aryl alkyl ketones via the formation of alkylzinc species from alkyl iodides followed by transmetallation and reductive elimination[380]. The Pd-catalyzed carbonylation of the diaryliodonium salts 516 under mild conditions in the presence of Zn affords ketones 517 via phenylzinc. The a-diketone 518 is formed as a byproduct[381],... 

Organotin compounds such as aryl-, alkenyl-, and alkynylstannanes are useful for the ketone synthesis by transmetallation of acylpalladium 529 and reductive elimination of 530 as shown[389-393]. Acetophenone (531) is obtained by the carbonylation of iodobenzene with Me4Sn. Diaryl ketones... 

The transmetallation of the siloxycyclopropane 751 with the aryl- or alke-nylpalladium 752 generates the Pd homoenolate 753. and subsequent reductive elimination gives the /3-aryl or alkenyl ketone 754[618]. It should be noted that the Pd homoenolate 753 generated in this reaction undergoes reductive elimination without d-elimination. 

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