Reduction chemoselective

The reductive chemoselective bis-silylation of quinones was afforded by thermal reaction with silyl tellurides. ... 

Reductions. Chemoselective reduction of aldehydes in the presence of ketones is quite general, except for very highly hindered aldehydes. 

Reductions. Chemoselective reduction of sulfoxides to sulfides and a-diketones to a-ketols employs the title reagent in MeCN at 0°. Aldehydes are dimerized to give 1,2-diols (dl- meso-) on exposure to Tifi, with or without adding Cu. ... 

Keywords Photocatalyst Titanium(IV) oxide Reduction Chemoselective ... 

Stereoselective and chemoselective semihydrogenation of the internal alkyne 208 to the ew-alkene 210 is achieved by the Pd-catalyzed reaction of some hydride sources. Tetramethyldihydrosiloxane (TMDHS) (209) i.s used in the presence of AcOH[116]. (EtO)3SiH in aqueous THF is also effective for the reduction of alkynes to di-alkenes[l 17], Semihydrogenation to the d.v-alkene 211 is possible also with triethylammonium formate with Pd on carbon[118]. Good yields and high cis selectivity are obtained by catalysis with Pd2fdba)3-Bu3P[119],... 

Sodium cyanoborohydride is remarkably chemoselective. Reduction of aldehydes and ketones are, unlike those with NaBH pH-dependent, and practical reduction rates are achieved at pH 3 to 4. At pH 5—7, imines (>C=N—) are reduced more rapidly than carbonyls. This reactivity permits reductive amination of aldehydes and ketones under very mild conditions (42). 

Sodium cyanoborohydride has become important in biochemical appHcations that require hydrolytic stabiHty of the reducing agent and chemoselectivity, in sensitive molecules. It is also a preferred reagent for oxime reductions. 

A catalyst, usually acid, is required to promote chemoselective and regioselective reduction under mild conditions. A variety of organosilanes can be used, but triethylsilane ia the presence of trifiuoroacetic acid is the most frequendy reported. Use of this reagent enables reduction of alkenes to alkanes. Branched alkenes are reduced more readily than unbranched ones. Selective hydrogenation of branched dienes is also possible. 

Chemoselective reduction of a,(3-epoxy carbonyl compounds to aldols and their analogs by organoseleniums and its application to natural product synthesis 98YGK736. 

A stereochemical issue of great importance presents itself here. In the chemoselective reduction of the two ketone carbonyls at C-5 and C-8 in 6, the addition of hydride takes place on the same side... 

Scheme 4 outlines the synthesis of key intermediate 7 in its correct absolute stereochemical form from readily available (S)-(-)-malic acid (15). Simultaneous protection of the contiguous carboxyl and secondary hydroxyl groups in the form of an acetonide proceeds smoothly with 2,2 -dimethoxypropane and para-toluene-sulfonic acid and provides intermediate 26 as a crystalline solid in 75-85 % yield. Chemoselective reduction of the terminal carboxyl group in 26 with borane-tetrahydrofuran complex (B H3 THF) affords a primary hydroxyl group that attacks the proximal carbonyl group, upon acidification, to give a hydroxybutyrolactone. Treat-... 

Inherent in the reduction of asymmetrically substituted cyclic imides is the problem of regiose-lectivity. Imides, in which one carbonyl group is part of a (thio)carbamate or urea function, usually show complete chemoselectivity for reduction of the other carbonyl group, indicated with an arrow. 

Chemoselectivity in catalytic reductions depends solely on thermodynamic stability and the amide is much more... 

There is no problem of chemoselectivity here it is not possible to reduce the aliphatic NO group in (10) without reducing the aromatic NO group too. This is easily solved by introducing the aromatic nitro group after the reduction. 

The chemoselectivity of the ozonolysis is all right because ozone attacks the most electron-rich double bond, that is the one furthest from the carbonyl group in (17, R=H). Reductive work-up is again needed after the ozonolysis,... 

Reduction of carbon-carbon double bond Microalgae easily reduce carbon-carbon double bonds in enone. Usually, the reduction of carbonyl group and carbon-carbon double bond proceeds concomitantly to afford the mixture of corresponding saturated ketone, saturated alcohol, and unsaturated alcohol because a whole cell of microalgae has two types of reductases to reduce carbonyl and olefinic groups. The use of isolated reductase, which reduces carbon-carbon double bond chemoselectively, can produce saturated ketones selectively. 

Another example from the Ciba-Geigy group concerns the chemoselective reductive dehalogenation of 2,2,4-trichlorobutanal to 2,4-dichlorobutanol (Eqn. (4)), a herbicide intermediate (Bader et al., 1996). 

The rate of hydrozirconation of a terminal olefin is much faster than the reduction of the oxirane ring. This chemoselectivity was used in the preparation of various cycloalkylmethanols by hydrozirconation of alkenyloxiranes (Scheme 8-28) [217]. 

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