Complex hydrides amines

The milder metal hydnde reagents are also used in stereoselective reductions Inclusion complexes of amine-borane reagent with cyclodexnins reduce ketones to opucally active alcohols, sometimes in modest enantiomeric excess [59] (equation 48). Diisobutylaluminum hydride modified by zmc bromide-MMA. A -tetra-methylethylenediamme (TMEDA) reduces a,a-difluoro-[i-hydroxy ketones to give predominantly erythro-2,2-difluoro-l,3-diols [60] (equation 49). The three isomers are formed on reduction with aluminum isopropoxide... 

Opening of a bottle where some particles of lithium aluminum hydride were squeezed between the neck and the stopper caused a fire [68]. Lithium aluminum hydride must not be crushed in a porcelain mortar with a pestle. Fire and even explosion may result from contact of lithium aluminum hydride with small amounts of water or moisture. Sodium bis(2-methoxy-ethoxy)aluminum hydride (Vitride, Red-Al ) delivered in benzene or toluene solutions also may ignite in contact with water. Borane (diborane) ignites in contact with air and is therefore kept in solutions in tetrahydrofuran or in complexes with amines and sulfides. Powdered lithium borohydride may ignite in moist air. Sodium borohydride and sodium cyanoborohydride, on the other hand, are considered safe. ... 

Ketimines are reduced to amines very easily by catalytic hydrogenation, by complex hydrides and by formic acid. They are intermediates in reductive amination of ketones (p. 134). An example of the reduction of a ketimine is conversion of 3-aminocarbonyl-2,3-diphenylazirine to the corresponding aziridine by sodium borohydride (yield 73%), by potassium borohydride (yield 71%) and by sodium bis (2-methoxyethoxy) aluminum hydride (yield 71%) [939]. 

Reduction of amides to aldehydes was accomplished mainly by complex hydrides. Not every amide is suitable for reduction to aldehyde. Good yields were obtained only with some tertiary amides and lithium aluminum hydride, lithium triethoxyaluminohydride or sodium bis 2-methoxyethoxy)aluminum hydride. The nature of the substituents on nitrogen plays a key role. Amides derived from aromatic amines such as JV-methylaniline [1103] and especially pyrrole, indole and carbazole were found most suitable for the preparation of aldehydes. By adding 0.25 mol of lithium aluminum hydride in ether to 1 mol of the amide in ethereal solution cooled to —10° to —15°, 37-60% yields of benzaldehyde were obtained from the benzoyl derivatives of the above heterocycles [1104] and 68% yield from N-methylbenzanilide [1103]. Similarly 4,4,4-trifluorobutanol was prepared in 83% yield by reduction of N-(4,4,4-trifluorobutanoyl)carbazole in ether at —10° [1105]. 

The predominant application of reduction of amides lies in their conversion to amines, realized most often by hydrides and complex hydrides. Primary,... 

Hydroxylamines can be synthesized from various aliphatic and aromatic nitro compounds by reduction with metals and other one-electron donors, with complex hydrides and other two-electron donors, and by hydrogenation. In all cases the reduction proceeds stepwise and, depending on reaction conditions, can provide both amines and hydroxylamines. 

The widely used reduction of thiopyrylium salts to thiopyrans has been accomplished with complex hydrides. Alternative reductions with ethanol-amine mixtures or with trichlorosilane are rarely used. 

Reduction of aldehydes and ketones. Earlier work on amine borane reagents was conducted mainly with tertiary amines and led to the conclusion that these borane complexes reduced carbonyl compounds very slowly, at least under neutral conditions, and that the yield of alcohols is low. Actually complexes of borane with primary amines, NHj or (CH3)3CNH2, reduce carbonyl compounds rapidly and with utilization of the three hydride equivalents. BH3 NH3 is less subject to steric effects than traditional complex hydrides. A particular advantage is that NH3 BH3 and (CH3)3CNH2 BH3 reduce aldehyde groups much more rapidly than keto groups, but cyclohexanone can be reduced selectively in the presence of aliphatic and aromatic acyclic ketones. 

These complexes have been used as starting materials in the preparation of other alkoxy and phenoxy complexes, phenylimido complexes, analogous amine complexes, dioxotetrapyridinerhenium(V) salts and dioxobis(ethylene-diamine) rhenium (V) salts, cyano complexes of rhenium-(V), acetylacetone complexes, hydrides, carbonyls, and isonitrile complexes. The products of reactions using the materials described here as sources are normally easier to purify than those obtained by other methods. 

Transition-metal-coordinated NjR complexes react with complex hydrides to form NHNR complexes or free NHj or amines in reactions whose stoichiometries are not established ... 

Complex hydride reductions of Nj, N O, [CN] and nitriles in reactions containing complex mixtures of metal-ion species produce N—H bonded products " by reactions that may relate to those of the biological nitrogenases". Complete reaction stoichiometries are not well established. These reactions are not competitive with other methods for NH or amine synthesis. Nitrogen reacts in H O with a mixture of NaBH, S-donor ligands (e.g., NH CjM SH) and Mo and Fe salts to form NHj and NjH in low yield . In similar systems, nitriles and isonitriles are reduced to NHj and amines in low yield . 

Chemically, methods for deoxygenation and reductive deamination have seen additions in the last two decades which depart from those traditional approaches using hydride reduction of activated alcohols and diazene generation from aliphatic amines. New methods for amine activation, new complex hydrides and, in particular, methods using electron transfer and free radical processes have greatly expanded the range of substrate molecules which can be subject to efficient functional group removal. 

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