Aromatic ketone reductions

However, most frequently used methods for reduction of aromatic ketones to hydrocarbons are, as in the case of other ketones, Clemmensen reduction [160, 161, 758, 843, 844] Procedure 31, p. 213), Wolff-Kizhner reduction [280,281,282, 759, 774,845] Procedure 45, p. 216), or reduction of p-toluene-sulfonylhydrazones of the ketones with lithium aluminum hydride [811, 812] or with borane and benzoic acid [786]. 

The reduction of aldehydes and ketones. Aromatic hydrocarbons are the main products when aromatic aldehydes or ketones are reduced with amalgamated zinc and concentrated hydrochloric acid (the Clemmensen reduction, e.g. hexylbenzene, Expt 6.3). 

Reductive amination. Conversion of ketones or aldehydes to amines is usually accomplished by reduction of the carbonyl compound with sodium cyanoborohydride in the presence of an amine (Borch reduction, 4, 448-449). However, yields are generally poor in reactions of hindered or acid-sensitive ketones, aromatic amines, or trifluoromethyl ketones. Yields can be improved markedly by treatment of the ketone and amine first with TiCl4 or Ti(0-i -Pr)42 in CH2C12 or benzene to form the imine or enamine and then with NaCNBH3 in CH3OH to effect reduction. Note that primary amines can be obtained by use of hexamethyldisilazane as a substitute for ammonia (last example). 

Reduction of alkyl aryl ketones. Aromatic ketones can be reduced to the corresponding hydrocarbons by reaction with LiAlH4 and P2I4 in refluxing benzene. The ketone and the two reagents are used in equimolar amounts. Yields range from 45 to —100%. The method offers a mild alternative to Clemmensen and Wolff-Kishner reductions. 

Reduction of ketones.1 Reduction of one carbonyl group requires 2 moles of this complex because B2H6 is also released. Aliphatic ketones are reduced readily, but aromatic ketones are reduced much more slowly, and a,(3-enones even more slowly. Consequently some selective reductions are possible. 

Reductive dimerization of ketones Aromatic -unsaturated ketones are reduced and dimerized to 1,5-hexadienes by sequential reaction with LiAIH4, Fe3(CO)i2, and HCl. The effectiveness of iron carbonyls shows the order Fe3(CO), 2 > Fe2(CO)y > FeiCO). ... 

Enantioselective Reduction of Aromatic Ketones. Aromatic substituted ketones and a-halo ketones are reduced by (EtO>3 SiH with good enantioselectivity in the presence of bis-oxazoline titanium complex [Ti(ciY-DiPh-Box)2F2], prepared from chiral bis-oxazoline, BuLi, and Tip4 (eq 4). 

A complex Zn(BH4)2-1.5 DMF has been described [HJl]. This shows a greater selectivity than Zn(BH4)2 in diethylether and does not react with the a-enones. In MeCN, this complex allows the reduction of aldehydes in the presence of ketones, the reduction of some sterically unhindered ketones in the presence of other less accessible ketones, or even the reduction of aliphatic ketones in the presence of aromatic ones (Section 3.2.1). 

The cyanophosphates prepared from a,P-unsaturated or aromatic ketones are reductively cleaved with lithium in liquid ammonia at low temperature. When the reduction is carried out under refluxing conditions (at -33°C) in the presence of t-BuOH, the methylene compound is obtained in quantitative yield by loss of the cyanophosphate group (Scheme 6.45). In contrast, quenching the reaction mixture at low temperature with isoprene leads to the unsaturated nitrile, resulting from dephosphorylation, as an epimeric mixture. ... 

The sertraline precursor is a chiral alcohol with the stereogenic centre adjacent to an aromatic ring. An obvious approach is to make the hydroxyl group by asymmetric reduction of the corresponding ketone. CBS reduction is a possibility, as is a ruthenium-catalysed hydrogenation using the ligand TsDPEN (p. 1115 of the textbook). 

Nitroaromatics R—NO2 Ketones —CO— Reduction Aromatic hydroxylamines Amines, aromatic R—NH2... 

Two waves arise with the indicated half-wave potentials. The wave height for the process P2 + Zb -> P3 occurring at the more negative potential will obviously depend on the rate at which electroactive P2 is generated from Pi, which is itself assumed to be electroinactive. Examples where this type of behavior arises are the reductions of a-substituted ketones, aromatic bicarbonyl compounds such as p-diacetylbenzene, terephthaldialdehyde and a,/8-unsaturated ketones. Restricting ourselves to one type of example discussed by Zuman, " the following is the scheme for reduction of an a-substituted... 

SchifT s bases A -Arylimides, Ar-N = CR2, prepared by reaction of aromatic amines with aliphatic or aromatic aldehydes and ketones. They are crystalline, weakly basic compounds which give hydrochlorides in non-aqueous solvents. With dilute aqueous acids the parent amine and carbonyl compounds are regenerated. Reduction with sodium and alcohol gives... 

Aromatic ketones undergo this type of reduction particularly readily. 

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