Amines from oxime hydrogenation

Asymmetric catalytic reduction reactions represent one of the most efficient and convenient methods to prepare a wide range of enantiomerically pure compounds (i.e. a-amino acids can be prepared from a-enamides, alcohols from ketones and amines from oximes or imines). The chirality transfer can be accomplished by different types of chiral catalysts metallic catalysts are very efficient for the hydrogenation of olefins, some ketones and oximes, while nonmetallic catalysts provide a complementary method for ketone and oxime hydrogenation. 

Platinum oxide hydrogen chloride Amines from oximes... 

Hydrogen sulfide-sodium alcohol Amines from oximes s. 11, 29... 

The most general method for synthesizing amines involves the reduction of oximes and imine derivatives obtained from aldehydes or ketones (see Sections 5.5.2 and 4.3.11). By catalytic hydrogenation or by LiAltLj reduction, while 1° amines are prepared from oxime or unsubstituted imine, 2° amines are obtained from substituted imine. Unsubstituted imines are relatively unstable, and are reduced in situ. 

The product of this reaction is an oxime resulting from 1,2-addition of hydroxylamine to the carbonyl followed by dehydration. Please note that in the dehydration step, the amine contributes a hydrogen to match the leaving hydroxide group. The mechanism is illustrated below using arrow pushing. 

Use is made of the facile hydrogenation of nitro groups to prepare a-hydroxy primary amines from nitromethane-ketone addition products (Eqn. 19.22). The addition of a little acetic acid to the reaction medium can sometimes improve the yield. The p-hydroxyamines are more easily prepared in this way than by the hydrogenation of the corresponding cyanohydrin. a-Chloro nitro compounds are selectively hydrogenated to the oxime over palladium under... 

The stereochemistry of the amines obtained on hydrogenation of cyclic oximes is dependent on the pH of the reaction medium in the same way as the formation of alcohols from cyclic ketones, which was discussed in Chapter 18. In... 

CH—NHOH) to oxime (C=NOH) and ultimately to the nitroalkane (CH—NO2). Hydrogen peroxide generates amine oxides from tertiary cycloaUphatic... 

In non-polar solvents many aminolysis reactions show a third-order dependence on the amine, B. This may be explained by catalysis of leaving-group departure by hydrogen-bonded homoconjugates, BH+B. Evidence for this pathway has been adduced from studies of the reactions of some nitro-activated (9-aryl oximes (7) with pyrrolidine in benzene, chlorobenzene, and dioxane, and with piperidine and hexylamine in cyclohexane. The third-order dependence on amine of the reaction of 2,6-dinitroanisole with butylamine in toluene and toluene-octanol mixtures has been interpreted in terms of a mechanism involving attack by dimers of the nucleophile. ... 

If the addition of hydrogen takes place in a 1,2-mode the products are oximes, hydroxylamines, amines, and carbonyl compounds resulting from the hydrolysis of the oximes [567], Oximes and carbonyl compounds also result from reductions of a,/3-unsaturated compounds with iron [569, 570] and an oxime was prepared by catalytic hydrogenation of a )S-nitrostyrene derivative over palladium in pyridine (yield 89%) [571]. 

The nitro group is converted to versatile functionalities. A carbon-carbon double bond can be produced from nitroalkane by elimination of a nitro group with vicinal hydrogen as nitrous acid. The Nef reaction is also often used for transformation from nitroalkanes to ketones. The most useful chemical modification of a nitro group is the reduction furnishing oximes and amines, and further chemical conversion to various functionalities can be performed via diazonium salts. 

Asymmetric hydrogenation offers a useful synthetic route to chiral amines. Although the mechanism is unknown, only the (7%/V-acetyl-1 -arvlalkylamine 21 with 95% ee was obtained by the hydrogenation of a mixture of ( )- and (Z)-enamides 20a and 20b using Rh-Me-DuPHOS (XI). The A-acetvl enamines 20a,b are prepared by the reduction of oximes with Fe powder in acetic anhydride [21]. Also the acetamide 23 was obtained from 22 [22]. 

The conversion of nitrocoumarins into the amino compounds has been achieved by hydrogen transfer (95JCR(S)372) and an intramolecular hydride transfer features in the formation of Mannich bases of 4-aminocoumarins from 4-alkylaminocoumarin-3-carbaldehyde (95S633). Amine derivatives of coumarin-3-carboxaldehyde undergo a thermal 1,3-cycloaddilion involving an oxime nitrone isomerisation on reaction with Al-methyl-hydtoxylamine yielding hetero-fused coumarins (95JCS(P1)1857). 

Reeve and Christian compared Raney Ni and Raney Co (W-7 type) for the hydrogenation of six aliphatic and aromatic aldoximes and ketoximes in the presence or absence of ammonia.26 From the results summarized in Table 8.1, it is notable that Raney Co gives high yields of primary amine in ethanol or dioxane without addition of ammonia as seen in the results with butyraldoxime, 2-butanone oxime, and acetophenone oxime. On the other hand, Raney Ni usually requires an ammoniacal solvent for best results, with the exception of acetophenone oxime, which gave high yields of primary amine in the absence of ammonia. 

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