Other Reduction Reactions

Catalytic reductive coupling of epoxides (82, R1 = alkyl) with aldehydes (83) yields /3-hydroxy ethers (84), in a C-0 bond-forming process involving yields up to 90%.311 The reaction is catalysed by (Ph3P)3RuCl, a species which cannot reduce the aldehyde 

DFT has been used to explore the mechanism of reductive etherification of aromatic aldehydes by alcohols, using BH3 as catalyst and reductant.312 The reaction is suggested to proceed by addition (rate controlling), followed by reduction, and is expected to be feasible in polar solvents such as acetonitrile. 

Stabilized nucleophiles have been added to allylic alcohols using catalytic electronic activation , in which a reaction has been designed where an alcohol is temporarily oxidized to a carbonyl compound.313 

Aldehydes have been catalytically hydrogenated to alcohol products in a range of supercritical solvents under otherwise mild conditions.314 

The redox chemistry of quinones has been reviewed in the context of hydrogen bonding, protonation, and supramolecular effects that can modify their reactivity.315 

The kinetics and mechanism of hydride transfer between Michler s hydride and 2,3,5,6-tetrabromo-/3-benzoquinone have been investigated spectrophotometrically, examining both solvent and pressure effects.330 

A dynamic kinetic resolution has been employed to achieve a catalytic asymmetric reductive amination of aldehydes.332 Reductive amination of ketones and aldehydes by sodium triacetoxyborohydride has been reviewed, highlighting its advantage over other reagents.333 

Reductive amination of ketones using p-anisidine and the Hantzsch ester for transfer hydrogenation is a low-yielding reaction in toluene at room temperature, but thiourea is an efficient catalyst, and yields of up to 94% are reported at 50 °C.334 A mechanism involving thiourea hydrogen bonding to the intermediate imine is supported by ab initio calculations. 

A variety of activated carbonyls such as a-keto esters, benzils, cyclohexane-1,2-dione, and a-ketophosphonates have been reduced to the corresponding a-hydroxy compounds in THF at room temperature, using alkylphosphines (PMe3 or PPhMe2).335 

2H- and 180-labelling experiments suggest that proton transfer from alkylphosphine occurs (via e.g. 111 ), with aqueous workup releasing the product plus R2P(=0)Me. 

Ammonia borane acts as a metal-free reductant for ketones and aldehydes in methanol solution, via the MeOH BHj complex.In THF, borate esters are the only organic products, with dissociation of ammonia from ammonia borane being rate determining. H-, B-, and C-NMR studies, deuterium labelling, and kinetic isotope effects are 

A Brpnsted acid-catalysed decarboxylative redox amination converts 2-carboxyindoline (145) to an A-alkylindole (146), with an aldehyde as the source of the alkyl group.  

A review covers redox reactions of a-functionalized aldehydes catalysed by NHCs.  

A short review describes recent approaches to bifunctional iron catalysis of the hydrogenation of ketones.  

Iron pincer complexes (147), easily prepared from 2,6-bis(diisopropyl-phosphinomethyl)pyridine and iron(III) bromide, are excellent catalysts for hydrogenation of acetophenones and have been characterized by X-ray crystallography and H- and 3 P-NMR. 2 

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The bacteria in the intestinal tract serve as another well-known source of luminal drug degradation [61], though this is only important for the colon region as the luminal concentration of bacteria is 104 to 109-fold higher in the colon compared with the small intestine. Thus, this aspect is only relevant for drugs that reach this region, for example, due to poor permeability, slow dissolution or delivery by modified-release formulations. Hydrolytic and other reductive reactions are predominantly mediated by bacterial enzymes, and a list of the most prominent types... 

Asymmetric Catalytic Hydrogenation and Other Reduction Reactions... 

ASYMMETRIC CATALYTIC HYDROGENATION AND OTHER REDUCTION REACTIONS... 

Esters are completely reduced to alcohols whde unsaturated esters are converted to unsaturated alcohols. Other reduction reactions include conversion of phenyl isocyanate to N-methylanihne ... 

Other reduction reactions are possible for solutions with pH below 7, i.e., under acidic conditions, such as... 

Reduction of carbonyl groups, reduction of alcoholic groups and carbon-carbon double bonds, reduction of nitrogen-containing functional groups, other reductive reactions... 

Other reduction reactions may be involved in the abiotic degradation of synthetic organics. Such reactions commonly involve atoms or groups in the organic that are... 

In a sense Fd, rather than NADP+, is the direct recipient of electrons from PSI. For example, much of the reduced Fd is used to reduce NADP+, but some is used for other reductive reactions, too, such as the reduction of thioredoxin (Figure 17.23). Ferredoxin can also use electrons to reduce substances and may also be considered the final electron accepting molecule of PSI. 

Other reduction reactions also result in the formation of primary amines. For example, the catalytic reduction of a nitrile forms a primary amine. (Recall that a nitrile can be obtained from the reaction of cyanide ion with an alkyl halide.)... 

Other reduction reactions are possible, depending on the nature of the solution to which the metal is exposed. For an acid solution having dissolved oxygen, reduction according to... 

Lin G-Q, Li Y-M, Chan ASC. Asymmetric catalytic hydrogenation and other reduction reactions. In Principles and applications of asymmetric synthesis. New York Wiley 2001. p 331-389. 

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