Big Chemical Encyclopedia

Chemical substances, components, reactions, process design ...

Articles Figures Tables About

Carbonyl compounds metal hydride reduction

Asymmetric reduction of carbonyl compounds can usually be achieved either through direct catalytic hydrogenation or by metal hydride reduction. It should be mentioned here that reduction of carbonyl compounds by catalytic hydrogenation may not be chemoselective. Other co-existing functional groups such as the C=C bond may also undergo hydrogenation. [Pg.355]

When a proton source such as ethanol is used, sodium reduces esters, aldehydes and ketones to alcohols and the reduction is known as Bouveault-Blanc reduction s . But metal hydride reduction of carbonyl compounds gives higher yields of alcohols. [Pg.255]

The new metallic hydrides are excellent reducing agents for carbonyl compounds. These hydrides now include lithium aluminum hydride, lithium borohydride, and sodium borohydride. The last reagent may be used in either aqueous or methanolic solutions. It does not reduce esters, acids, or nitriles and, for this reason, is superior for certain selective reductions. Other groups which are unaffected by this reagent include a,/S-double bonds and hydroxyl, methoxyl, nitro, and dimethylamino groups. ... [Pg.526]

The introduction of tritium into molecules is most commonly achieved by reductive methods, including catalytic reduction by tritium gas, PH2], of olefins, catalytic reductive replacement of halogen (Cl, Br, or I) by H2, and metal pH] hydride reduction of carbonyl compounds, eg, ketones (qv) and some esters, to tritium-labeled alcohols (5). The use of tritium-labeled building blocks, eg, pH] methyl iodide and pH]-acetic anhydride, is an alternative route to the preparation of high specific activity, tritium-labeled compounds. The use of these techniques for the synthesis of radiolabeled receptor ligands, ie, dmgs and dmg analogues, has been described ia detail ia the Hterature (6,7). [Pg.438]

The key step in the reduction of a carbonyl compound by either LiAlH4 or NaBH4 is the transfer of a hydride ion from the metal to the carbonyl carbon. [Pg.464]

Rhin(bpy)3]3+ and its derivatives are able to reduce selectively NAD+ to 1,4-NADH in aqueous buffer.48-50 It is likely that a rhodium-hydride intermediate, e.g., [Rhni(bpy)2(H20)(H)]2+, acts as a hydride transfer agent in this catalytic process. This system has been coupled internally to the enzymatic reduction of carbonyl compounds using an alcohol dehydrogenase (HLADH) as an NADH-dependent enzyme (Scheme 4). The [Rhin(bpy)3]3+ derivative containing 2,2 -bipyridine-5-sulfonic acid as ligand gave the best results in terms of turnover number (46 turnovers for the metal catalyst, 101 for the cofactor), but was handicapped by slow reaction kinetics, with a maximum of five turnovers per day.50... [Pg.477]

Tributyltin hydride reduction of carbonyl compounds. The reduction of carbonyl compounds with metal hydrides can also proceed via an electron-transfer activation in analogy to the metal hydride insertion into TCNE.188 Such a notion is further supported by the following observations (a) the reaction rates are enhanced by light as well as heat 189 (b) the rate of the reduction depends strongly on the reduction potentials of ketones. For example, trifluoroacetophenone ( re<1 = —1.38 V versus SCE) is quantitatively reduced by Bu3SnH in propionitrile within 5 min, whereas the reduction of cyclohexanone (Erea — 2.4 V versus SCE) to cyclohexanol (under identical... [Pg.252]

One approach to enantioselective reduction of prochiral carbonyl compounds is to utilize chiral ligand-modified metal hydride reagents. In these reagents, the number of reactive hydride species is minimized in order to get high chemo-selectivity. Enantiofacial differentiation is due to the introduced chiral ligand. [Pg.356]

Sodium dithionite is well established [ 1 ] as a powerful reducing agent under alkaline conditions. Its redox potential is close to that of sodium borohydride [2] and, in several respects, there are advantages in the use of sodium dithionite as an alternative to the metal hydrides under phase-transfer catalytic conditions, particularly in the reduction of carbonyl compounds [3],... [Pg.495]

This complex can also transfer hydride to another molecule of the carbonyl compound in a similar manner, and the process continues until all four hydrides have been delivered. Since all four hydrogens in the complex metal hydride are capable of being used in the reduction process, 1 mol of reducing agent reduces 4 mol of aldehyde or ketone. Finally, the last complex is decomposed by the addition of water as a proton source. [Pg.236]

Allylic acetates are usually prepared by esterification from allylic alcohols. However, the corresponding alcohols are often only accessible by the fairly expensive hydride reduction of carbonyl compounds. Consequently, direct allylic functionalization of easily available olefins has been intensively investigated. Most of these reactions involve peroxides or a variety of metal salts.However, serious drawbacks of these reactions, (e.g. toxicity of some metals, stoichiometric reaction conditions, or nongenerality) may be responsible for their infrequent use for the construction of allylic alcohols or acetates. [Pg.184]

The present preparation illustrates a general and convenient method for a two-step deoxygenation of carbonyl compounds to olefins. Related procedures comprise the basic decomposition of p-toluenesulfonylhydrazones, the hydride reduction of enol ethers, enol acetates, enamines, the reduction of enol phosphates (and/or enol phosphorodiamidates) by lithium metal in ethylamine (or liquid ammonia),the reduction of enol phosphates by titanium metal... [Pg.199]

CO into a metal-hydrogen bond, apparently analogous to the common insertion of CO into a metal-alkyl bond (6). Step (c) is the reductive elimination of an acyl group and a hydride, observed in catalytic decarbonylation of aldehydes (7,8). Steps (d-f) correspond to catalytic hydrogenation of an organic carbonyl compound to an alcohol that can be achieved by several mononuclear complexes (9JO). Schemes similar to this one have been proposed for the mechanism of CO reduction by heterogeneous catalysts, the latter considered to consist of effectively separate, one-metal atom centers (11,12). As noted earlier, however, this may not be a reasonable model. [Pg.158]

They proposed a polymerization scheme closely related to other well-known chemical reactions of metal alkoxide with carbonyl compounds (20). In Scheme 2, complex [A] is converted to [B] by hydride ion transfer from the alkoxyl group to the carbon atom of aldehyde (Meerwein-Ponndorf reduction). Addition of one molecule of monomer to the growing chain requires transfer of the alkoxide anion to the carbonyl group to form a new alkoxide [C]. Repetition of these two consecutive processes, i.e., coordination of aldehyde and transfer of the alkoxide anion, constitutes the chain propagation step. [Pg.61]

Metal hydrides usually reduce the carbonyl to alcohol but LAH converts xanthone into a dixanthyl ether (454) or xanthene (453) according to the conditions. The latter product is also obtained by the Wolff-Kishner-Huang-Minlon reduction. Metal-liquid ammonia opens the pyran-4-one ring of chromones and flavones to form dihydrochalcones and other compounds (79JOC1494). [Pg.705]

By Reduction of Unsaturated Precursors The method of choice for labeling with tritium is the reduction of a suitable unsaturated precursor (containing a double bond, carbonyl group, etc.) with carrier-free tritium gas or tritiated metal hydrides. The major limitation of this method is the availability of a suitable unsaturated precursor of the desired compound. It is essential to carry out the synthesis in a non-hydroxylic solvent (dioxane, ethyl acetate, etc.). Reductions carried out in alcohol or water will lead to almost complete exchange of the tritium gas with the solvent. [Pg.100]


See other pages where Carbonyl compounds metal hydride reduction is mentioned: [Pg.188]    [Pg.108]    [Pg.314]    [Pg.524]    [Pg.646]    [Pg.188]    [Pg.443]    [Pg.289]    [Pg.34]    [Pg.164]    [Pg.297]    [Pg.31]    [Pg.731]    [Pg.270]    [Pg.367]    [Pg.447]    [Pg.114]    [Pg.144]    [Pg.89]    [Pg.299]    [Pg.264]    [Pg.195]    [Pg.96]    [Pg.164]    [Pg.533]    [Pg.20]    [Pg.71]    [Pg.297]   


SEARCH



Carbonyl compounds hydride reduction

Carbonyl compounds metal hydrides

Carbonyl compounds metalation

Carbonyl compounds reduction

Carbonyl compounds, reductive

Carbonyl reduction

Hydride carbonyl reduction

Hydride compounds

Hydride compounds reduction

Metal carbonyl hydrides

Metal carbonyls reduction

Metal hydride reduction

Reduction carbonylation

© 2024 chempedia.info