1,2,3-Triketones diketones

PurpurogaHin (5), a red-brown to black mordant dye, forms from electrolytic and other mild oxidations of pyrogaHol (1). The reaction is beHeved to proceed through 3-hydroxy-(9-benzoquinone (2) and 3-hydroxy-6-(3,4,5-trihydroxyphenyl)-(9-benzoquinone (3). The last, in the form of its tautomeric triketonic stmcture, represents the vinylogue of a P-diketone. Acid hydrolysis leads to the formation of (4), foHowed by cyclization and loss of formic acid... 

Table 2 Effect of 1,3-Diketones or Triketone on AAM Polymerization Initiated by Ce(IV) Ion...

In this example, the /3-diketone 2-methyJ-l,3-cyclopentanedione is used to generate the enolate ion required for Michael reaction and an aryl-substituted a,/3-unsaturated ketone is used as the acceptor. Base-catalyzed Michael reaction between the two partners yields an intermediate triketone, which then cyclizes in an intramolecular aldol condensation to give a Robinson annulation product. Several further transformations are required to complete the synthesis of estrone. 

As in 10-104, a ketone attacks with its second most acidic position if 2 mol of base are used. Thus, P-diketones have been converted to l,3,5-triketones. ° ... 

Diketones are reductively cyclized in a TFA-catalyzed reaction. The cycliza-tion of the cage structure shown in Eq. 236 illustrates this ring closure in the formation of an acetal of trifluoroacetaldehyde.409 The organosilane reduction of triketone 69 followed by Jones oxidation gives the cyclic ketoether in fair yield (Eq. 237).410... 

Conjugate addition of RN02 to enones. Primary nitroalkanes and a, (3-enones when activated by alumina form conjugate addition products that are oxidized in situ by alkaline hydrogen peroxide to 1,4-diketones. A similar reaction of nitromethane with a vinyl ketone provides 1,4,7-triketones. 

Aromatic esters may be used to aroylate the dianions derived from 1,3-diketones by reaction with potassium amide (60JOC538). Not only are acetyl and benzoyl acetones suitable for reaction, but alicyclic diketones and 2-hydroxyacetophenone are also acceptable. Cycliz-ation of the triketones occurs in cold sulfuric acid, presumably via the enolic form and the hemiacetal (Scheme 132). 

The direct condensation of pentan-3-one with ethyl formate failed to give 3,5-dimethyl-pyran-4-one. Instead, the diketone was produced, the enolate of which is apparently of insufficient reactivity to undergo condensation with a second molecule of ester. However, the isopropyl derivative (407) of the enol condensed with ethyl formate, and the potential triketone cyclized to the pyran-4-one (408) under acid conditions (Scheme 133) (64JOC2678). 

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... 

This procedure appears to be fairly general for the aroylation of /3-diketones to give 1,3,5-triketones. Using this method, the submitters2 have aroylated benzoylacetone with methyl benzoate (87%), methyl />-chlorobenzoate (78%), and ethyl nicotinate (69%). Also, acetylacetone has been monobenzoylated with methyl benzoate to form l-phenyl-l,3,5-hexanetrione in 75% yield or dibenzoylated with the same ester to form 1,7-diphenyl-... 

On the pages which follow, general methods are illustrated for the synthesis of a wide variety of classes of organic compounds including acyl isocyanates (from amides and oxalyl chloride p. 16), epoxides (from reductive coupling of aromatic aldehydes by hexamethylphosphorous triamide p. 31), a-fluoro acids (from 1-alkenes p. 37), 0-lactams (from olefins and chlorosulfonyl isocyanate p. 51), 1 y3,5-triketones (from dianions of 1,3-diketones and esters p. 57), sulfinate esters (from disulfides, alcohols, and lead tetraacetate p. 62), carboxylic acids (from carbonylation of alcohols or olefins via carbonium-ion intermediates p. 72), sulfoxides (from sulfides and sodium periodate p. 78), carbazoles... 

Ozonolysis of diketone carbonate 417 in methanol afforded an almost quantitative yield of the bicyclic diene triketone hydroxy-ester 418 (119). This remarkable transformation can also be readily explained. Ozonolysis of 417 produces the tetraketone intermediate 419 followed by methanol addition to produce the hemi-ketal 420 which undergoes a retro-Claisen reaction to 421. Then, loss of carbon dioxide from 421 yields 418. Again, 420 could also undergo a Grob type fragmentation to yield 418 directly. 

Heating a solution of the triketone 1 in DME containing a catalytic amount of p-TsOH under reflux for 48 hours results in quantitative isomerisation to 2. Treatment of a THF solution of 1 with t-BuOK/t-BuOH at room temperature for 16 hours, on the other hand, gives a 78% yield of the diketone 3. 

Combining aldol and Michael reactions in one sequence is very powerful, particularly if one of the reactions is a cyclisation. The Robinson annelation9 makes new rings in compounds like 73 that were needed to synthesise steroids. Disconnection of the enone reveals triketone 74 having 1,3- and 1,5-dicarbonyl relationships. The 1,3-disconnection would not remove any carbon atoms but the 1,5-disconnection at the branchpoint gives a symmetrical 3-diketone that should be good at conjugate addition. 

On treatment with acetic anhydride in pyridine, the yellow tetraketone (68), the yellow triketone (66), and the diketone (67) afforded monoacetyl, diacetyl, and triacetyl derivatives, respectively. All these derivatives contained a tertiary acetoxyl group. However, comparisons of 1H-NMR spectra of the parent ketones with those of the acetyl derivatives indicated that a rearrangement of the molecule or a major conformational change must have occurred. On the basis of extensive H-NMR spectral analysis, structure 69 was proposed for the diacetyl derivative which was derived from the triketone 66. Structure 69 was justified on the basis of conformational arguments. 

In contrast with previous reports, Sodeoka s reaction conditions were applicable to a variety of /8-ketoesters (Scheme 2) [5]. With the Pd aqua complex 3, the Michael adducts were obtained in high yield with high enantioselectivity. For example, the reaction of the /8-ketoester 4 with less reactive /3-substituted enones such as 3-penten-2-one proceeded smoothly to give 5 in 99 % ee. In this reaction, catalytic asymmetric construction of the highly crowded vicinal tertiary and quaternary carbon centers was achieved in one step. Furthermore, the reaction of 1,3-diketones with enones was successfully performed, and the desired triketone 6 was obtained in good yield and with 90 % ee. In contrast, conventional basic conditions (tertiary amines, alkoxides, or ammonium hydroxides) gave complex mixtures, probably because of the instability, under the basic conditions, of the triketone produced. This result clearly indicates that the reaction using the Pd aqua complex 3 is quite mild. 

As already indicated, 1,3,5-triketones react anomalously with hydrazines. Interaction of the sodium enolate of a diketone and an a-halogenohydrazone, however, leads to the monohydrazone of a... 

Phenylation and arylation have also been performed in bifunctional compounds such as malonates, /1-diketones and /1-ketoesters (Table 8.4). Diethyl malonate was arylated at room temperature affording mixtures of mono- and bis-arylated products, whereas isopropylidene malonate (Meldrum s acid) underwent bis arylation directly. Dimedone, the all carbon analogue of Meldrum s acid, was also mono-and bis-phenylated, with some concomitant O-phenylation [33], Generally, / -diketones show often ambident reactivity but the O-arylated product is normally the minor one an exception was noted in the triketone (PhCO)2CHCOPh which underwent mainly O-phenylation (68%) [33], Several dianions from /1-diketones have been arylated in high yields at the a-position, in a procedure superior to other methods [35]. 

Phenyliodonium /S-diketonates underwent ozonolytic fragmentation, providing a useful synthesis of unsolvated v/c-triketones in high yields. 

Base catalysis is not required for conjugate addition. If the nucleophile is sufficiently enolized under the reaction conditions then the enol form is perfectly able to attack the unsaturated carbonyl compound. Enols are neutral and thus soft nucleophiles favouring conjugate attack, and p-dicarbonyl compounds are enolized to a significant extent (Chapter 21). Under acidic conditions there can be absolutely no base present but conjugate addition proceeds very efficiently. In this way methyl vinyl ketone (butenone) reacts with the cyclic P-diketone promoted by acetic acid to form a quaternary centre. The yield is excellent and the triketone product is an important intermediate in steroid synthesis as you will see later in this chapter. 

The mechanism combines two important reactions and we shall take it step by step, The first stage is the formation of the stable enolate, here of the 1,3-diketone, and the conjugate addition to the enone. The enolate of the product is in equilibrium with the triketone. 

Single acylation reactions of dianionic cuprates have already been shown in Table 4. After the acylation reactions of these cuprates with one equivalent of an acyl chloride, the resulting lithium enolates can be subjected to a second acylation or alkylation28. The first example shown in Scheme 18 demonstrates such a case, in which the second acylation using benzoyl chloride gave a triketone (Scheme 18). The second example deals with the treatment of the enolate with iodomethane, which resulted in the corresponding 2-methyl-1,4-diketone. 

Compartmental ligands (16) are derived from diketonates and triketonates and are usually synthesized from Schiff base reactions of the ketone with a diamine. ... 

The presence of S-carbonyl groups with at least one proton on the carbon between them allows a keto/enol tautomerism to occur and, under appropriate conditions, the eno-lic proton can be removed. The S-5-tricarbonyl compounds are the higher analogues of the / -diketonates and can take triketone, monoenol and dienol forms in their tautomeric equilibrium (equation 86) accordingly, they can behave as bidentate or tridentate ligands to form metal chelate complexes. ... 

Another area where metal /3-diketonates have made a significant impact is in the oxidation of aLkanes , alkenes and alcohols A number of different metal complexes have been used in these reactions, including Pd(acac)2 (29) , Co(acac)3 (30) , Fe(acac)3 (31), a bimetallic Pd(II) complex containing a 1,3,5-triketone ligand, MCI (acac)(PPh3) (32) where M = Ni, Co, Cu, Mn(acac)3 (33) , Mo02(acac)2 (34) , VO (acac)2 (35) and VO(hfac)2 (36) . In the latter study, the oxidation of a-acetylenic... 

Therefore several reactions were subjected to various antibody catalyses, e. g., ester and enol ether cleavage, transesteiification, ketone reduction. Cope rearrangement, ring closure via epoxide opening, or Diels-Alder cycloaddition [74, 75]. An exceptional reaction is the antibody-catalyzed Robinson annulation of triketone 28 to the Wieland-Miescher ketone 29 on a preparative scale. Surprisingly, even the alkylation of diketone 27 with methyl vinyl ketone was catalyzed by the same antibody, but at moderate rates (Scheme 15) [76]. 

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