Structure, of 1,3-diketones

Because the structure of 1,3-diketones comprise a methylene group between two activating carbonyls, equilibrium is shifted toward the enol form. The equilibrium distribution varies with structure and solvent (303,306) (Table 13). The enol forms are cyclic and acidic and form covalent, colored, solid chelates with metals ... 

Strontium nitrate, for preparation of strontium sulfate or strontium selenite, 3 17 Strontium selenide, 3 20 phosphors, 3 11, 22 Strontium selenite, for preparation of strontium selenide, 3 20 Strontium sulfate, for preparation of strontium sulfide, 3 19 Strontium sulfide, 3 20 phosphors, 3 11, 21, 23 Structure, of 1,3-diketones, 2 10 electronic, of rare earth elements, 2 30... 

Structure of 1,3-Diketones. The 1,3-diketones exist in two tautomeric forms, keto and enol ... 

Katsumura, Kitaura and their coworkers [74] found and discussed the high reactivity of vinylic vs allylic hydrogen in the photosensitized reactions of twisted 1,3-dienes in terms of the interaction in the perepoxide structure. Yoshioka and coworkers [75] investigated the effects of solvent polarity on the product distribution in the reaction of singlet oxygen with enolic tautomers of 1,3-diketones and discussed the role of the perepoxide intermediate or the perepoxide-Uke transition state to explain their results. A recent review of the ene reactions of was based on the significant intervention of the perepoxide structure [76], which can be taken as a quasi-intermediate. 

The chemistry of 1,3-diketone complexes of nonmetallic elements (B, Si, Ge, Sb, Te) has been reviewed.68 Condensation of acetylacetone with TeCl4 yields Te(CH2COCH2COCH2)Cl2 (8a), which may be reduced to Te(CH2COCH2COCFI2) (8b). The crystal structures of these compounds demonstrate an unusual coordination of tellurium to the terminal carbons of the diketonate.61 72 In the dichloride complex, Teiv exhibits a distorted trigonal bipyramidal geometry with a stereochemi-cally active lone electron pair in the equatorial plane. In S2(MeCOCHCOMe)2 the acetylacetonate methine carbons are bonded to a disulfur unit.73... 

Triketones are homologues of 1,3-diketones and in these, too, keto-enol tautomerism has been probed by H NMR spectroscopy.567,568 Triketones and tetraketones may coordinate to one or more metal ions per molecule. In the latter case the metal centers are held in such close proximity that, in some cases, interesting magnetic effects may be observed. Structural and magnetic properties of polynuclear transition metal jS-polyketonates have been thoroughly reviewed.569,570... 

Zelenin and co-workers have shown (85KGS854, 85KGS1000 86KGS128 87KGS1210 88ZOR426) that the reaction products of 1,3-diketones with hydrazides in a molar ratio of 1 2 most frequently possess the cyclic structure of the corresponding 5-hydrazino-2-pyrazolines (such as 76B). They can also be produced in the reactions between the corresponding hydrazine derivatives and l-acyl-5-hydroxy-2-pyrazolines or 1-acyl-5-methylene-2-pyrazolines. 

The reduction of aldols and ketols from the aldol condensation (method 102) is often a convenient route to branched 1,3-dio/s. Catalytic hydrogenation over platinum oxide, nickel-on-kieselguhr, and copper-chromium oxide has been used. Other procedures include electrolytic reduction and reduction by aluminum amalgam. 1,3-Diols may also be prepared by catalytic reduction of 1,3-diketones. Cleavage of the carbon-to-carbon and carbon-to-oxygen bonds accompanies this conversion. The effect of structure on the course of the reaction has been studied. ... 

The methods of preparation and purification of metal derivatives of 1,3-diketones have been described in a previous volume. Because of the interest in the structure " and reactions of metal derivatives of /3-keto imines, RC0CH2C(=NR )R", it is desirable to consider the methods of preparation of these compounds. Inasmuch as /3-keto imines are closely related to 1,3-diketones and to salicylaldimines, o-HOC6H4CH==NR, the methods of preparation show similarities. Although this review is concerned principally with /3-keto imines, some comparisons with 1,3-diketones and salicylaldimines are made. 

Kel in, A. V., Maioli, A. Recent advances in the chemistry of 1,3-diketones Structural modifications and synthetic applications. Curr. Org. Chem. 2003, 7, 1855-1886. 

The structures, types, properties, uses, nomenclature, and general methods of preparation of metal derivatives of 1,3-diketones have been discussed in a previous volume.1 It now seems desirable to consider in somewhat more detail the various factors involved in the preparation and purification of these substances. 

Most of die binding site residues are conserved in the plant and rat enzymes and the x-ray structures of the different enzyme-inhibitor complexes are very similar, with little movement of the protein backbone (Figure 3). In the apo structure, two histidines, a glutamic acid and three water molecules coordinate the active site metal ion. In the inhibitor bound structures, the 1,3-diketone of the inhibitor chelates the metal ion, replacing two of the water molecules. There... 

In this region occur the broad bands of many acidic hydrogens. Carboxylic acid dimers absorb broadly near 3000 cm" with satellite bands near 2650 and 2550 cm . Amine salts absorb in this region. Their bands have much fine structure. Phosphorus acids absorb broadly in this region. The strongly bonded hydrogen in the enol form of 1,3-diketones and related compounds absorbs broadly at 3100-2700 cm ... 

Digitoxigenin, structure of, 1097 Digitoxin, structure of, 989 Dihalide, alkynes from, 261 Dihedral angle, 94 Diiodomelhane. Simmons-Smith reaction with, 228-229 Diisobutylaluminum hydride, reaction with esters, 812 structure of, 699 Diisopropylamine, pK.d of, 923 1,3-Diketone, pfCa of, 852 Dimethyl disulfide, bond angles in, 20 structure of, 20 Dimethyl ether, electrostatic... 

A different approach to quinoxalines and heterocycle-fused pyrazines has been described by the Lindsley group, based on the cyclocondensation of 1,2-diketones and aryl/heteroaryl 1,2-diamines (Scheme 6.260) [450]. Optimized reaction conditions involved heating an equimolar mixture of the diketone and diamine components for 5 min at 160 °C in a 9 1 methanol/acetic acid solvent mixture, which furnished the substituted quinoxalines in excellent yields. This approach could also be applied equally successfully to the synthesis of heteroaryl pyrazines, such as pyr-ido[2,3-b]pyrazines and thieno[3,4-b]pyrazines. The same group has employed 1,2-diketone building blocks for the preparation of other heterocyclic structures (see Schemes 6.198, 6.268, and 6.269). 

Chambers RD, Fox MA, Sandford G (2005) Elemental fluorine - Part 18. Selective Direct Fluorination of 1,3-Ketoesters and 1,3-Diketones using Gas/ Liquid Microreactor Technology. Lab Chip 5 1132-1139 Cheng RP, Gellman SH, DeGrado WF (2001) Beta-Peptides From Structure to Function. Chem Rev 101 3219-3232... 

Proton and 13C NMR spectral data of 33 derivatives of 64 have been tabulated and assigned <1996MRC409>. Several 3-oxo derivatives of 64 have been studied by proton and 13C NMR spectroscopy as part of a comprehensive investigation of their structural and spectroscopic properties <2003BCJ2361>. The regioselectivity of the formation of the six-membered ring in derivatives of 67 from 1,3-diketones has been established by proton NMR spectroscopy and nuclear Overhauser effects <1997CHE535>. 

On treating diisobutene with acetic anhydride and anhydrous zinc chloride, A. C. Byrns and T. F. Doumani had isolated in 1943 a crystalline compound to which they had ascribed the structure of a zinc complex with a 1,3-diketone 40 the correct pyrylium chlorozincate structure was established by A. T. Balaban et al.41 in 1961, after extended investigation on the formation of pyrylium salts by alkene diacylation.42 This formation again had remained undetected for many decades during which alkenes had been acylated but only the water-insoluble monoacylation products had been investigated, whereas the water-soluble pyrylium salts went into the sink with the Lewis or Bronsted acid catalysts that had been used in the acylation. 

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