Ketone a-hydroxy

Certain ketoximes can be converted to nitriles by the action of proton or Lewis acids. Among these are oximes of a-diketones (illustrated above), a-keto acids, a-dialkylamino ketones, a-hydroxy ketones, p-keto ethers, and similar compounds. These are fragmentation reactions, analogous to 17-25 and 17-26. For example, ot-dialkylamino ketoximes also give amines and aldehydes or ketones besides nitriles. 

The oxidation may proceed through the hydrated form of the carbonyl group > CH(OH)2. The rate of oxidation is 1,2-glycols > a-hydroxy aldehydes > a-hydroxy ketones > a-hydroxy acids. 

Reduction of a-silyloxy ketones. a-Hydroxy ketones are reduced by zinc boro-hydride with the expected anf/-selectivity, the extent of which varies somewhat with the substitution pattern. Preparation of the isomeric, v /i-diols can be effected by reduction of the a-r-butyidiphenylsilyloxy ketones with SMEAH in toluene at —78° followed by desilylation (equation I). Again, the selectivity varies with the nature of R and R-, and is low when R is a bulky alkyl group. 

Stereoselective reduction of acyclic ketones. a-Hydroxy ketones (1) are reduced by Zn(BH4)2 selectively to the anti,vic-d o 2. In contrast, the t-butyldiphenylsilyloxy derivative of 1 is reduced selectively to the. vyn,vic-diol 3 by sodium bis(2-methoxy-ethoxy)aluminum hydride. ... 

FENYL-a-HYDROXYBENZYLKETON a-HYDR-OXYBENZYLPHENTL KETONE a-HYDROXY-o-PHENYLACETOPHENONE 2-HYDROXY-2-PHENYH ACETOPHENONE KETONE, O-HYDROXYBENZYL PHENYL NCI-C50011 WY-42956... 

KETONE, HEPTYL 4-PYRlDYL see HBF600 KETONE, a-HYDROXY BENZYL PHENYL see BCP250 KETONE, 7-(2-HYDROXY-3-... 

Periodic Acid Test for vic-Glycols. Vicinal glycols (hydroxyl groups on adjacent carbon atoms) can be detected by reaction with periodic acid. In addition to 1,2-glycols, a positive test is given by a-hydroxy aldehydes, a-hydroxy ketones, a-hydroxy acids, and a-amino alcohols, as well as 1,2-diketones. 

Asymmetric synthesis by means of a cyandiydrin is an imprvtant process in organic synthesis, because the cyanohydrin can be easily converted into a variety of valuable synthetic intermediates, such as a-hy-droxy ketones, a-hydroxy acids, y-diketones, p-amino alcohols, 4-oxocarboxylic esters, 4 xonitriles, a-amino acids and acyl cyanides. More specifically, the (S)-cyanohydrin of m-phenoxybenzaldehyde is a building block for the synthesis of the insecticide deltamethrin, or (IR)-cis-pyrethroids. ... 

The selenium-stabilized carbanions derived by deprotonation of selenoacetals by strong bases, such as a mixture of KDA-lithium r-butoxide, LiTMP in HMPT/THF or LBDA in THF at -78 °C, react readily with a variety of electrophiles including primary or secondary halides, epoxides, ketones, aldehydes and enones, followed by deprotection, to give ketones, 3-hydroxy ketones, a-hydroxy ketones and 1,4-dicarbonyl compounds respectively. - - ... 

Reduction of a-alkoxy ketones a-Hydroxy ketones are reduced by Sml2 in THF/CH3OH in rather low yield ( 30%). In contrast a-acetoxy ketones are reduced in >75% yield. A simple expedient is to reduce the a-hydroxy ketone in the presence of AC2O with Sml2 (equation I). a-Silyloxy, benzoyloxy, and tosyloxy... 

Powerful oxidants (for example chromic acid or permanganate ion) can bring about, under vigorous conditions, the oxidation of ketones, although this usually leads to cleavage of the carbon chain adjacent to the carbonyl group (with formation of carboxylic acids) and is rarely used in synthesis. More important are controlled methods of oxidation leading to a,p-unsaturated ketones, a-hydroxy-ketones or lactones (without rupture of the molecule). 

Reduction of a-Ketolsf Carbonyl compounds containing a-hydroxy, a-acetoxy, or a-halo groups react with excess TMS-I to give the parent ketone. a-Hydroxy ketone reductions proceed via the iodide, which is then reduced with iodide ion to form the parent ketone (eq 32). 

The addition of lithium and Grignard reagents to isocyanides which do not contain a-hydrogens proceeds by an a-addition to uoduce a metalloaldimine (7, an acyl anion equivalent). The lithium aldimines ate versatile reagents which can be used as precursors the preparation of aldehydes, ketones, a-hydroxy ketones, a-keto acids, a- and -hydroxy acids, silyl ketones and a-amino acids (Scheme... 

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