Hydroxycarboxylic acids, carbonyl compounds

Most of the carbonyl compounds discussed in this section are either pyran-2- or -4-ones but a small number of pyran-3-ones and chroman-3-ones are known <77HC(31)193>. Tetrahy-dropyran-2-ones are lactones of 5- (or S-) hydroxycarboxylic acids and are not discussed in detail. 

An aldol addition involves the addition of the a-C atom of a carbonyl compound, a carboxylic acid, a carboxylic ester, or a carboxylic amide to the C=0 double bond of an aldehyde or a ketone. The products of aldol additions are /3-hydroxylcarbonyl compounds (aldols), /i-hydroxycarboxylic acids, /Thydroxycarboxylic esters, or j3-hydroxycarboxylic amides. 

A number of reactions of phosphorus pentachloride (78) with carbonyl compounds have been reported. a-Hydroxycarboxylic acids, such as malic and tartaric acids, react with (78) to give phosphorodichloridates with general part-structure (110). The heterocyclic hydrazide (111) is converted into the cyanide (112), and hence into the isomer (113), by treatment with (78) in refluxing benzene. ... 

Peterson aikenation of carbonyl compounds with trimethylsilylmethoxymethyl carbanion (14) can also give enol ethers. An example is the reaction of (14) with adamantanone. Another method of alkene synthesis is the elimination of CO2 and H2O from a P-hydroxycarboxylic acid. If the carboxylic acid is substituted by an a-alkoxy group, the reaction can be used for the synthesis of enol ethers, as illustrated in Scheme 4. ... 

HYDROXY-3-ALKYLCYCLOPENT-2-ENE-1-ONES Sulfuric acid. a-HYDROXY CARBONYL COMPOUNDS m-Chloroperbenzoic acid. a-HYDROXYCARBOXYLIC ACIDS f-Butyldimethylsilyl cyanide. 

Sodium cohalt carbonylate / -Hydroxycarboxylic acid esters from oxido compounds... 

Raw or gently pasteurised milk (e.g. for 10 seconds at 73 °C) has a fine characteristic odour and sweet taste. Typical components present in low concentrations are dimethylsulfide, biacetyl, 2-methylbutan-l-ol, (Z)-hept-4-enal and ( )-non-2-enal. Milk pasteurised at higher temperatures and Ultra High Temperature (UHT) milk present the so-called cooked flavour, the appearance of which is the first measurable manifestation of the chemical changes that occur in heated milk. The substances responsible for the cooked off-flavour are sulfane and other sulfur compounds. Of particular importance are dimethylsulfide, dimethyldisulfide and dimethyltrisullide that are produced from proteins contained in the membranes of fat particles and from thiamine. Also relevant are alkane-2-ones (methylketones) generated by thermal decarboxylation of P-oxocarboxylic acids (mainly hexane-2-one, heptane-2-one and nonane-2-one), y-lactones and 5-lactones produced by dehydration of y- and 5-hydroxycarboxylic acids (mainly 8-decalactone and y- and 8-dodecalactones). Important carbonyl compounds include biacetyl, hexanal, 3-methylbutanal, (Z)-hept-4-enal and ( )-non-2-enal. In the more intensive thermal treatment of milk (sterilisation), products of the Maillard reaction play a role, such as maltol and isomaltol, 5-hydroxymethylfuran-2-carbaldehyde, 4-hydroxy-2,5-dimethyl-2 f-furan-3-one (furaneol) and 2,5-dimethylpyrazine. 

A-Iodosuccinimide reacts with a-hydroxy-carboxylic acids in an oxidative decarboxylation sequence to give carbonyl compounds. A dehydrative decarboxylation of 2,3-disubstituted 3-hydroxycarboxylic acids, using dimethyl-formamide acetals, has been reported. Photosensitized oxygenation of diethyl... 

In the mid-2000s, Griengl and coworkers reasoned that a small molecule with a similar pK as HCN, for example, nitromethane, could act as nucleophile for addition to carbonyl compounds (nitroaldol or Henry reaction Scheme 25.3) [111]. The Henry reaction is a classical name reaction in organic chemistry for the formation of C—C bonds. The resulting p-nitro alcohols can be transformed to nitroalkenes, 2-nitroketones, a-hydroxycarboxylic acids, and 1,2-amino alcohols. Although several other enzymes and proteins such as hydrolases and lipases [112], transglutaminase... 

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