3,3-Dimethyl-2,4-pentanedione

In order to synthesize the topologically equivalent metallacryptate 65 in an analogous manner to 64, the w-phenylene spacer was substituted by an m-pyridylene spacer. Deprotonation of l,l -(2,6-pyridylene)bis-l,3-(4-dimethyl)pentanedione 63... 

Meldrum s acid, pK 7.4, is exceptionally acidic in comparison to an acyclic analog such as dimethyl malonate, pK 15.9. For comparison, 5,5-dimethyl-1,3-cyclohexane-dione is only moderately more acidic than 2,4-pentanedione (11.2 versus 13.43). The pK values are those for DMSO solution. It is also found that the enhanced acidity of Meldrum s acid derivatives decreases as the ring size is increased. Analyze factors that could contribute to the enhanced acidity of Meldrum s acid. 

The straightforward construction of substituted pyrone 4 proceeded as follows (see Scheme 6c). Alkylation of the monoanion of 2,4-pentanedione (8) with methyl iodide furnishes 3-methyl-2,4-pentanedione. Conversion of this substance into the corresponding dianion with sodium amide followed by selective carboxylation of the more basic site provides intermediate 7. Pyrone 4 is obtained after cyclization with l,l -carbonyldiimidazole and methylation of the resulting enol with dimethyl sulfate. 

Figure 1 Transfer chemical potentials for selected iron complexes from water into aqueous methanol (on the molar scale, at 298 K). Ligand abbreviations not appearing in the list at the end of this chapter are acac = acetylacetonate (2,4-pentanedionate) dmpp = l,2-dimethyl-3-hydroxy-4-pyridinonate, the anion from (24) malt = maltolate (2-methyl-3-hydroxy-4-pyranonate, the anion from (233)).

Papai et al. selected as model reaction the addition of 2,4-pentanedione (acetylacetone) to trans-(R)-mtrostyvQnQ, catalyzed by the bifunctional thiourea catalyst shown in Scheme 6 [46]. The analogous Michael-addition involving dimethyl malonate and nitroethylene as substrates, and a simplified catalyst was calculated at the same level of theory by Liu et al. [47]. Himo et al. performed a density functional study on the related cinchona-thiouTQa catalyzed Henry-reaction between nitromethane and benzaldehyde [48]. 

The photochemistry of a number of long chain aliphatic a-diketones has been reported.46 68 Included in the study were 2,3-pentanedione, 3,4-hexane-dione, 4,5-octanedione, 5,6-decanedione, 2,7-dimethyl-4,5-octanedione, and 1,2-cyclodecanedione. Without exception, irradiation of these compounds in cyclohexane or benzene yielded cyclobutanols, presumably by an internal abstraction-cyclization mechanism. The reaction is quite selective, producing... 

PENTANEDIONE, 3,3-DIMETHYL-1,5-DIPHENYL-, 65, 12 Pentane, 2,2,4-trimethyl-4-mtroso-, 65, 166... 

The reaction works well for 2,7-dimethyl-4,5-octanedione, 4,5-octane-dione, and 3,4-hexanedione (110). Irradiation of 2,3-pentanedione... 

Ketone Peroxides. These materials are mixtures of compounds with hydroperoxy groups and are composed primarily of the two structures shown in Table 2. Ketone peroxides are marketed as solutions in inert solvents such as dimethyl phthalate. They are primarily employed in room-temperature-initiated curing of unsaturated polyester resin compositions (usually containing styrene monomer) using transition-metal promoters such as cobalt naphthenate. Ketone peroxides contain the hydroperoxy (—OOH) group and thus are susceptible to the same hazards as hydroperoxides. By far the most popular commercial ketone peroxide is methyl ethyl ketone peroxide [1338-23-4]. Smaller quantities of ketone peroxides such as methyl isobutyl ketone peroxide [28056-59-9], cyclohexanone peroxide [12262-58-7], and 2,4-pentanedione peroxide [37187-22-7] are used commercially (47). 

DIICTHYL-l, 5-DIPHENYLPENTANE-l, 5-DIOHE (1,5-Pentanedione, 3,3-dimethyl-1,5-diphenyl-)... 

Dimethyl-7>IV-[1,2,5]oxatellurazoIo[2,3-6][l,2,5]oxatellurazole 6.5 g (50 mmol) of 2,4-pentanedione dioxime and 8.8 g (55 mmol) of tellurium dioxide are added to a mixture of 180 ml of xylene and 20 ml of pcntanol and the resultant mixture is heated under reflux for 24 h. The solvents are then evaporated under vacuum, the residue is dissolved in the minimum amount of benzene, and this solution is chromatographed on a column of silica gel with benzene as the mobile phase. The orange colored band is collected, the solvent is evaporated, and the residue is recrystallized from cyclohexane yield 2.5 g (20%) m.p. 145°. 

Yogurt 2,3-Butanedione, acetaldehyde, hexanoic acid, dimethyl sulfide, 2,3-pentanedione 43... 

As Section IV will be mostly devoted to 2,4-pentanedione, acacH, it is worthwhile to dwell on this well studied species. The rate of interconversion between the keto and the enol form of acacH is rather slow at room temperature , thus they can be simultaneously detected by NMR spectroscopy it has been observed that the lower the polarity of the solvent, the higher the percentage of the enol tautomer . Electron diffraction studies indicate that in the gas phase acacH adopts the enol configuration with a keto/enol ratio of 8/92. More recently, an X-ray analysis of acacH, carried out at 110 showed that it exists as a mixture of the two enol forms 86 and 87, with the enolic hydrogen atom equally distributed over two positions close to the oxygen atoms as in 88. It should be noted that inclusion compounds containing different host molecules show different ratios of acacH in the enol form. For example, acacH exists as a dynamically averaged 1 1 mixture of 86 and 87 in an inclusion complex with l,T-binaphthyl-2,2 -dicarboxylic acid as host , while l,l-bis( >-hydroxyphenyl)cyclohexane and (4R,5R)-trawi-4,5-bis(hydroxydiphenylmethyl)-2,2-dimethyl-l,3-dioxolane include acacH in pure enolic form. ... 

Bis(2,4-pentanedionato)diaquocobalt(II) was first obtained b Gach by warming 2,4-pentanedione (acetylacetone) with precipitated cobalt(II) hydroxide. Jones prepared the compound by adding 2,4-pentanedione to an aqueous solution of hexaamminecobalt(II) ion. Recent workers have employed the method of Charles and Pawlikowski, which consists of adding sodium acetate solution to a water-methanol solution of cobalt(II) chloride and 2,4-pentanedione, followed by recrys-tallization from methanol. Bullen grew crystals from dimethyl-formamide for an x-ray diffraction study. 

When a metal ion such as nickel (II) is absent, thiazoles and mercaptals are formed. Such reactions have been carried out in which the diketone was biacetyl, 2,3-pentanedione, 2,3-octanedione, l-phenyl-l,2-propane-dione, and 1,2-cyclohexanedione (51). In like manner, the tris complexes of W,W -dimethyl-2,3-butane diimine with iron(II), cobalt(II), and nickel(II) may be prepared from methylamine and biacetyl when the appropriate metal ion (27j 28j 41) is present. Replacing methylamine with hydroxylamine causes the formation of a-dioximes (13). 

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