Alcohols by reduction of carbonyl

Preparation of Alcohols by Reduction of Carbonyl Functional Groups... 

Table 7.1. Preparation of alcohols by reduction of carbonyl compounds.

Alcohols are generally prepared on insoluble supports by reduction of carbonyl compounds or by addition of carbon nucleophiles to carbonyl compounds, although other strategies have also been used (Figure 7.1). 

In some circumstances, the production of a 2-halo alcohol by reduction of the carbonyl group of an a-halo ketone with metal hydrides is a useful synthetic reaction ... 

Alcohols are easily accessible by reduction of carbonyl compounds, such as aldehydes, ketones or carboxylic acid derivatives. While aldehydes, ketones and esters have been frequently used in microwave-assisted reductions, there have been no reports about the use of microwave technology in the reduction of nitriles or amides. 

Ionic routes to allylic (2) and benzylic (4) alcohols use reduction of carbonyl compounds (1) and (3) since these are readily available by condensation or Friedel-Crafts reaction. 

Carboxylic acids and their esters are converted into the corresponding alcohols by reduction of their carbonyl group to a methylene group, and three methods are available for this purpose, namely ... 

By Reduction of Carbonyl Compounds. Use of high (10 kbar) pressures has been shown to effect trialkylstannane reductions of ketones in the absence of radical initiators or Lewis acids.10 Zinc borohydride has been demonstrated to be a mild reducing agent for the conversion of benzenethiol esters into alcohols in good yield. Use of mixed solvents containing methanol has been found to confer some chemoselectivity upon reductions with lithium borohydride and permits enhanced rates of reduction of esters, lactones, and... 

Many biological processes involve oxidation of alcohols to carbonyl compounds or the reverse process reduction of carbonyl compounds to alcohols Ethanol for example is metabolized m the liver to acetaldehyde Such processes are catalyzed by enzymes the enzyme that catalyzes the oxidation of ethanol is called alcohol dehydrogenase... 

Alcohols can be prepared from carbonyl compounds by reduction of aide hydes and ketones See Table 15 3... 

Table 17 2 summarizes the reactions of aldehydes and ketones that you ve seen m ear her chapters All are valuable tools to the synthetic chemist Carbonyl groups provide access to hydrocarbons by Clemmensen or Wolff-Kishner reduction (Section 12 8) to alcohols by reduction (Section 15 2) or by reaction with Grignard or organolithmm reagents (Sections 14 6 and 14 7)... 

Hydroxypyrroles. Pyrroles with nitrogen-substituted side chains containing hydroxyl groups are best prepared by the Paal-Knorr cyclization. Pyrroles with hydroxyl groups on carbon side chains can be made by reduction of the appropriate carbonyl compound with hydrides, by Grignard synthesis, or by iasertion of ethylene oxide or formaldehyde. For example, pyrrole plus formaldehyde gives 2-hydroxymethylpyrrole [27472-36-2] (24). The hydroxymethylpyrroles do not act as normal primary alcohols because of resonance stabilization of carbonium ions formed by loss of water. 

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). 

Reductive amination ol aldehydes or ketones by cyanoborohydride (or tnacetoxyborohydride) anion Selective reduction of carbonyls to alcohol, oximes to N alkylhydroxylarmnes, enamines to amines... 

The well-known reduction of carbonyl groups to alcohols has been refined in recent studies to render the reaction more regioselective and more stereoselective Per-fluorodiketones are reduced by lithium aluminum hydride to the corresponding diols, but the use of potassium or sodium borohydride allows isolation of the ketoalcohol Similarly, a perfluoroketo acid fluonde yields diol with lithium aluminum hydnde, but the related hydroxy acid is obtainable with potassium borohydnde [i f] (equations 46 and 47)... 

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