Aldehyde a-hydroxy

The polyhydric alcohols of Solubility Group II are liquids of relatively high boiling point and may be detected inter alia by the reactions already described for Alcohols (see 6). Compounds containing two hydroxyl groups attached to adjacent carbon atoms (1 2-glyeols), a-hydroxy aldehydes and ketones, and 1 2-diketones may be identified by the periodic acid test, given in reaction 9. 

Another reaction that is characteristic of a-hydroxy aldehydes or ketones, which has been found of value for the characterisation of sugars, is the formation of osazones with phenylhydrazine. This reagent reacts with either an aldose... 

Although alcohol dehydrogenases (ADH) also catalyze the oxidation of aldehydes to the corresponding acids, the rate of this reaction is significantly lower. The systems that combine ADH and aldehyde dehydrogenases (EC 1.2.1.5) (AldDH) are much more efficient. For example, HLAD catalyzes the enantioselective oxidation of a number of racemic 1,2-diols to L-a-hydroxy aldehydes which are further converted to L-a-hydroxy acids by AldDH (166). 

A carbonyl condensation reaction between two molecules of acetaldehyde yields a hydroxy aldehyde product. 

Cleavage of the oxathiane moiety can be carried out with iV-chlorosuccinimide/silver nitrate and leads to the a-hydroxy aldehyde 21 along with a diastereomeric mixture of sultines 20. The sultines can be reduced to the hydroxy thiol 22 which can be reconverted to the chiral auxiliary 16 in ail overall recovery of about 70%39. 

Cleavage of the addition product 5 can be easily performed by treatment with dilute ( 1 %) aqueous alcoholic hydrochloric acid which liberates the chiral amino alcohol 3 and an a-hydroxy aldehyde. The latter can be further oxidized to the oc-hydroxy carboxylic acid 6 with sodium chlorite33. 

Dithioacetal monoxide anions react with carbonyl compounds in a similar way affording the corresponding a-hydroxy aldehyde dithioacetal oxides 428. Ogura and Tsuchihashi, who performed this reaction for the first time using the anion of methyl methylthiomethyl sulphoxide 324, obtained in this way a series of a-hydroxyaldehydes 429504 (equation 257). 

However, in some cases azines can be converted to hydrazones by treatment with excess hydrazine and NaOH. Arylhydrazines, especially phenyl, p-nitrophenyl, and 2,4-dinitrophenyl, are used much more often and give the corresponding hydrazones with most aldehydes and ketones.Since these are usually solids, they make excellent derivatives and are commonly employed for this purpose. Cyclic hydrazones are also known, ° as are conjugated hydrazones. a-Hydroxy aldehydes and ketones and ot-dicarbonyl compounds give osazones, in which two adjacent carbons have carbon-nitrogen double bonds ... 

When the reaction is run with potassium fert-butoxide in THF at -5°C, one obtains (after hydrolysis) the normal Knoevenagel product (32), except that the isocyano group has been hydrated (16-65). With the same base but with DME as solvent the product is the nitrile (33). When the ketone is treated with 31 and thallium(I) ethoxide in a 4 1 mixture of absolute ethanol and DME at room temperature, the product is a 4-ethoxy-2-oxazoline (34). Since 33 can be hydrolyzed to a carboxylic acid and 34 to an a-hydroxy aldehyde, this versatile reaction provides a means for achieving the conversion of RCOR to RCHR COOH, RCHR CN, or RCR (OH)CHO. The conversions to RCHR COOH and to RCHR CN have also been carried out with certain aldehydes (R = H). 

If the reaction is carried out with ketone labeled in the C=0 group with the first pathway predicts that the product will contain all the " C in the C=0 carbon, while in the second pathway the label will be in the a carbon (demonstrating migration of oxygen). The results of such experiments have shown that in some cases only the C=0 carbon was labeled, in other cases only the a carbon, while in still others both carbons bore the label, indicating that in these cases both pathways were in operation. With a-hydroxy aldehydes and ketones, the process may stop after only one migration (this is called the a-ketol rearrangement). 

TKase can be used as a tool for the kinetic resolution of racemic a-hydroxy aldehydes. For example, D-glyceraldehydes shows 66% of the rate compared with... 

This method can be used in conjunction with addition of cyanide to prepare a-hydroxy aldehydes from ketones.90... 

It can be assumed that, in the presence of InCl3 and water, the cyclic enol ethers 2-618 form a hydroxy aldehyde which reacts with the aniline to give an aromatic im-inium ion. This represents an electron-poor 1,3-butadiene which can undergo a hetero-Diels-Alder reaction [323] with another molecule of 2-618 to give a mixture of the diastereomeric tetrahydroquinolines 2-619 and 2-620. 

This method has an analogy in the well known acyloin condensation, a reaction which takes place between two molecules of an aromatic aldehyde in a solution containing an alkali cyanide. Thus for example, benzaldehyde gives rise to benzoin, a compound in which the enediolic system, —C(OH)=C(OH)—, exists mainly in the ketonic form —CO—CHOH—. If a hydroxy aldehyde like D-glucose (X) is allowed to... 

An a-hydroxy aldehyde is attacked but the rate of oxidation is often low. ... 

An a-hydroxy aldehyde will be oxidized relatively rapidly if another hydroxyl group in a position 7 or 5 to the carbonyl permits formation of a pseudoglycol structure by cyclic hemiacetalization. ... 

Similarly, chiral nitrones (61a—c) and (62a—c) were obtained from the corresponding a-amino aldehydes (209, 210), nitrones (63a,b) from p-amino-a-hydroxy aldehydes (211), and chiral nitrones (64) and (65) from IV-fluorenyl-methoxycarbonyl (/V-Fmoc) amino acids and /V-Fmoc-dipeptides (Fig. 2.6) (212). 

Cyanohydrins are starting materials of widespread interest for preparing important compounds such as a-hydroxy acids/esters, a-amino acids, / -amino alcohols, a-hydroxy aldehydes, vicinal diols, and a-hydroxy ketones. Cyanohydrin compounds can be synthesized using various chiral catalysts such as cyclic... 

Oxidation of silyl enol ethers. Oxidation of silyl enol ethers to a-hydroxy aldehydes or ketones is usually effected with w-chloroperbenzoic acid (6, 112). This oxidation can also be effected by epoxidation with 2-(phenylsulfonyl)-3-( p-nitrophenyl) oxaziridine in CHC1, at 25-60° followed by rearrangement to a-silyloxy carbonyl compounds, which are hydrolyzed to the a-hydroxy carbonyl compound (BujNF or H,0 + ). Yields are moderate to high. Oxidation with a chiral 2-arene-sulfonyloxaziridine shows only modest enantioselectivity. 

The reaction was used for synthesis of (- )-norpseudoephedrine from a chiral a-hydroxy aldehyde (second example). The diastereoselectivity can be reversed by addition of alkyllithiums to a-trityloxy aldehydes, presumably because chelation with the oxygen atom is no longer possible. 

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