P-Hydroxycarbonyl compounds

A convenient procedure was developed for transformations of /V-siloxyisoxa-zolidines into functionalized p-hydroxycarbonyl compounds with aqueous titanium trichloride (185, 189) (Scheme 3.164). 

The aldol reaction is well established in organic chemistry as a remarkably useful synthetic tool, providing access to p-hydroxycarbonyl compounds and related building blocks. Intensive efforts have raised this classic process to a highly enantioselective transformation employing only catalytic amounts of chiral promoters, as reviewed in the previous section (Chap. 29.1). While some effective applications have been reported, most of the methodologies necessarily involve the preformation of latent enolates 2, such as ketene silyl acetals, using... 

The aldol reaction is one of the most useful and classical reactions in organic synthesis, since the resulting p-hydroxycarbonyl compounds are highly useful building blocks for pharmaceuticals and natural products.14 The asymmetric version of this reaction has been developed to a significant extent. We focus here on the asymmetric classical aldol reaction using a silver catalyst and related reactions.15... 

Another nucleophilic addition involving a charged nucleophile is the Aldol reaction. This involves the nucleophilic addition of enolate ions to aldehydes and ketones to form p-hydroxycarbonyl compounds ... 

Problem 17.20 Write structural formulas for the p-hydroxycarbonyl compounds and their dehydration products formed by aldol condensations of (a) butanal, b) phenylacetaldehyde, (c) diethyl ketone, (t/) cyclohexanone, (e) benzaldehyde. ... 

The Lewis acid mediated rearrangement of epoxy silyl ether (69) affords the corresponding P-hydroxycarbonyl compound (70 Scheme 26). ... 

Karrer, P. Hydroxycarbonyl compounds. I. A new synthesis of hydroxyaldehydes. Helv. Chim. Acta 1919, 2, 89-94. 

The direct asymmetric aldol reaction between unmodified aldehydes and ketones plays an important role in nature as a source of carbohydrates and it is used for the synthesis of chiral p-hydroxycarbonyl compounds. This reaction was performed by using (5)-proline/poly-(diallyldimethylammonium) hexafluorophosphate heterogeneous catalytic system 36. The catalyst was simply prepared by mixing a suspension of the commercially available polyelectrolyte 34 in methanol with a solution of (,S )-prolinc (35) in the same solvent (Scheme 3.11). 

Dehydration o1 primary nitro compounds (Mukeuyama reaction) affords nitrile oxides, which may dimerize to yield furoxans, or otherwise be trapped by suitable dipoiatophiles such as double or triple bond systems, leading to the formation of various heterocyclic systems, S. The latter have been used for further derivatization in the heterocyclic series, or in return as precursors of acyclic products after ring cleavage, for example, 1,3-amino alcohols 6 or p-hydroxycarbonyl compounds, 9. 

An important general reaction of enolate ions involves nucleophilic addition to the electrophilic carbonyl carbon atom of the aldehyde or ketone from which the enolate is derived. A dimeric anion 18 results, which may then be neutralized by abstraction of a proton to produce a p-hydroxycarbonyl compound, 19 (Eq. 18.10). If the reaction is performed in hydroxylic solvents such as water or an alcohol, the source of the proton may be the solvent, whose deprotonation will regenerate the base required for forming the enolate ion. Thus, the overall process is catalytic in the base that is used. 

The p-hydroxycarbonyl compound 19 is commonly called an aldol, and the reaction leading to its formation is referred to as an aldol addition. The term "aldol" reflects the fact that use of an aldehyde in the reaction provides a product... 

The aldol reaction is one of the most efficient carbon-bond forming reactions in organic chemistry. It combines an enol or an enolate with a carbonyl compound to yield a P-hydroxycarbonyl compound. Aldol reactions of simple... 

Two carbonyl compounds (1 and 3) can combine to form P-hydroxycarbonyl compounds (4) in the aldol reaction, discovered by Kane in 1838 (8). The addition of carbonyl compounds (1) to the imine (5) to form P-aminocarbonyl compounds (6), called the Mannich reaction, was discovered by Marie and Tollens in 1903 (Scheme 28.1) [9]. These synthetically and historically important break-... 

The aldol condensation uses aldehydes or ketones as substrates and yields p-hydroxycarbonyl compounds. 

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