24-Pentanedione carbon acidity

MalONIC ACID, ETHYLHYDROXY, DIETHYL ESTER, BENZOATE, 45, 37 Mfsitaidehydf, 47, 1 Mesitylcne, condensation with dichloro methyl methyl ether, 47, 1 Methalljl chloride in alkylation of 2,4-pentanedione with potassium carbonate, 47, 87... 

The Clemmensen reduction of j8-diketones (1,3-diketones) is rather complicated. The first step in the reaction of 2,4-pentanedione with zinc amalgam is an intramolecular pinacol reduction leading to a cyclopropanediol. Next the cyclopropane ring is opened in the acidic medium, and a rearrangement followed by a reduction gives the final product, a ketone, with a changed carbon skeleton [924, 925]. The ketone is usually accompanied by small amounts of the corresponding hydrocarbon [924] or an a-hydroxy ketone [925]. 

The most acidic hydrogen of 2,4-pentanedione is on the carbon between the two C=0 groups. If this hydrogen is removed, the new unshared electron pair of the conjugate base is delocalized onto both of the oxygens. The additional resonance stabilization causes this compound to be an even stronger acid. Its pKa is 9 it is a stronger acid than water. 

Iodine Potassium Iodide Dodecylbenzene Tridecyibenzene Hydroquinone Propionaldehyde Methylform amide Diacetone Alcohol Isoamyl Alcohol Pentanedione (2,4-) Acetylacetone Paraldehyde Butylaldehyde Butyraldehyde Levulinic Acid Dioctyl Adipate Acetic Acid Butyl Ester Butyl Acetate Dioxane (1,4-) Dioxane Dioxane (p-) Isoamyl Acetate Thiodiacetic Acid Butyl Stearate Santoprene 201-73 Kamax T-260 Adipic Acid Ethylene Chloroformate Caprylic Acid Octanoic Acid Hexamethylenediamine Butyl Carbitol Acetate Decane Carbon Dioxide Dimethylamine Sodium Methylate Freon 114B2 Tetrachloropentane Santicizer 141 Santoprene 201-64 Ecolan Hetron 99P Calcium Hydride Triton Sulfolane Tributyl Phosphate Tributylphosphate Sodium Diacetate Methacrylonitrile... 

The range of nucleophiles usable in this substitution reaction was very broad. Carbon nucleophiles such as acetoacetate, diethyl malonate, 3-methyl-2,4-pentanedione gave alkylated products in 98%, 94% and 86% yield, respectively. Nitrogen containing nucleophiles (hydrochloride salts of amino acids) gave Al-allylated products in 90-98% yield. Sodium phenylsulfmate and sodium azide also reacted in high yields (86% and 79%, respectively). The catalyst could be readily recovered and re-used. No loss of activity was observed over 7 continuous runs. 

Reaction of o-glucose with 2,4-pentanedione or ethylacetoacetate in the presence of ZnCl2 gave the respective D-arabino-tetrahydroxybutyl furans 7 and 8 [31] two sugar carbon atoms were utilized in building the furan ring. The alditolyl residues have been oxidatively cleaved to aldehyde or carboxylic acid and can be chemically modified to 9 to prepare hetarylene-carbopeptoid hbraries [32]. 

This approach has also been applied to the use of malonates as C-H acidic carbon pro-nucleophiles, observing that the reaction performed excellently with a wide range of different chalcones and (3-aryl substituted 2-butenones (Scheme 4.28). Moreover, other 1,3-dicarbonyl compounds and related derivatives such as malononitriles, (3-ketoesters, 2,4-pentanedione and ethyl nitroacetate have also been tested with success in the reaction using chalcone as Michael acceptor. In an independent work, the use of cyanoacetates was also surveyed with good results, although in this case mixtures of diastereoisomers were typically obtained. In all these cases, the stereochemical outcome of the reaction was consistent with the model proposed by Soos. 

If the a-carbon is between two carbonyl groups, the acidity of its a-hydrogen is even greater (Table 18.1). For example, the pK value for dissociation of a proton from the a-carbon of 2,4-pentanedione, a compound with an a-carbon between two ketone carbonyl groups, is 8.9. And the pK value for dissociation of a proton from the a-carbon of ethyl 3-oxobutyrate, which is between a ketone carbonyl group and an ester carbonyl group, is 10.7. Ethyl 3-oxobutyrate is classified as a j8-keto ester because the ester has a carbonyl group at the j8-position 2,4-pentanedione is a jS-diketone. 

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