1,2,3-Triketones cyclic

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... 

The autoxidation of cyclic ketones with dirhenium decacarbonyl under basic catalytic conditions produces dicarboxylic acids (68-73%) bicyclic ketones are converted into keto carboxylic acids and, when one ring is aromatic, quinones are obtained, e.g. 1-tetralone produces 2-hydroxy-1,4-naphthaquinone (93%), and H02C(CH2)4C0(CH2)3C02H (85%) is obtained from 1-decalone via a cyclic triketone [5]. 

The diacylation of isopropenyl acetate with anhydrides of dicarboxylic acids is applicable for the synthesis of several other cyclic jS-triketones in moderate yield. - It has been used for the synthesis of 2-acetylcyclohexane-l,3-dione (40% yield), 2-acetyl-4-methylcyclopentane-l,3-dione (10% yield), 2-acetyl-4,4-dimethylcyclopentane-l,3-dione (10% yield), 2-acetyl-5,5-dimethylcyclohexane-l,3-dione (10% yield), 2-acetylcyclo-heptane-l,3-dione (12% yield) and 2-acetylindane-l,3-dione (26% yield). Maleic anhydrides under more drastic conditions give acetylcyclopent-4-ene-l,3-diones in yields from 5% to 12%. The corresponding acylation of the enol acetate of 2-butanone with succinic anhydride has been used to prepare 2-methylcyclopentane-l,3-dione, an important intermediate in steroid synthesis. - ... 

If two cyclic 1,3-dioxo fragments are connected via a monocarbon 2,2 -bridge, only one undergoes cyclodehydration. Thus bicyclic 4//-pyran systems 20b (R = H or Ph) were obtained after the reaction of triketone 53... 

The synthesis of 3-methylsulfinylchroman-4-one (600) from ethyl salicylate follows a related pathway (72JHC171), whilst the triketone (601), derived from pentane-2,4-dione and the benzoate ester, exists as the substituted chromanone, a cyclic hemiacetal (81JOC2260). 

We shall consider the hydrate of the cyclic triketone, 18, known as ninhydrin, later in connection with amino acids ... 

When tellurium tetrachloride is condensed with diacetylacetone, CH3.CO.CH2.CO.CH2.CO.CH3, the triketone is transformed to di-methylpyrone, and the cyclic compound combines with tellurium tetrachloride and hydrogen chloride to form the oxonium salt dimethyl-pyrone tellurichloride,... 

Triketones are useful intermediates in the preparation of 4-pyrones, 4-pyridones,3,4 and other cyclic products. 

In conclusion, there have been many reports of the high synthetic potential of the intramolecular aldol reaction in the enantioselective construction of cyclic enones. In particular the proline-catalyzed desymmetrization of triketones has been widely used for formation of optically active bicyclic systems which are versatile building blocks for steroids and other biologically active compounds. 

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. 

Prior to the determination of the aldolase mechanism and the development of catalytic antibodies for the aldol reaction, Hajos and Parrish and independently Wiechert et al. discovered that (5)-proline catalyzes the intramolecular aldol reaction of cyclic triketones (Scheme 6.7). This is not only a catalytic effect the reaction proceeds with high yields and large enantiomeric excess. 

As pointed out some time ago, the electrochemistry of the dicopper complex of the series M2(l,3,5-triketonate)2 (140) posed some problems of interpretation. It was at first thought that the copper(II) complexes should display a single two-electron reduction [Cu(II)—Cu(II) Cu(I)—Cu(I)], with features of chemical reversibility in the short reaction times of cyclic voltammetry . Later, it was stated that they undergo a single two-electron reduction only in the presence of alkali metal ions. In the absence of such cations, the Cu2(l,3,5-triketonate)2 derivatives undergo the stepwise sequence Cu(II)—Cu(II) Cu(II)—Cu(I) Cu(I)—Cu(I), the second one-electron reduction being irreversible and located at rather negative potential values " . ... 

The most interesting and practical asymmetric induction process that involves enamines is the proline-catalyzed conversion of the prochiral triketone in Scheme 15 to the cyclic aldol condensation product" or to the aldol product. The course of the reaction is determined by the presence (or absence) of a strong acid such as hydrochloric acid as a cocatalyst. As a result of both the practical significance of the product(s) as synthetic intermediate(s) and the catalytic nature of this process, there has been a high level of interest directed at establishing the mechanistic pathway for these reactions. 

Another experimental result is also consistent with the hypothesis that cyclic 1,2,3-triketones are not stable. 2-Diazoindan-l,3-dione (9.91) is oxidized by eA butyl hypochlorite in ethanol to the 2-monoacetal 9.92 of indan-l,2,3-trione. The monoacetal undergoes hydrolysis to 2,2-dihydroxyindan-l,3-dione (ninhydrin hydrate 9.93), but the trione itself could not be identified (9-41). 

A second possibility of proving the structure of 38 consisted in the cleavage of the double bonds, the rungs of the M6bius- ladder , by ozonolysis [30]. While the cylinder 37 led to two 30-membered cyclic triketones 39, the Mobius strip 38 gave a 60-membered cyclic hexaketone 40. 

Du Pont started relatively late in the triketone field, and directed their efforts toward novel fused bicyclic acids. As a result of their work in this area, they discovered the broad leaf weed cereal herbicide ketospiridox [58] (62, proposed common name. Fig. 4.3.10). Ishihara, inspired by earlier work of Hokko [59], identified some new benzoyl analogues with cyclic acetal meta-substituents (63 and 64, Fig. 4.3.11) that they claim have good pre-emergent activity in flooded rice paddy fields without damaging the rice seedlings [60]. 

The mechanism involves acid-catalysed conversion of the keto form of the cyclic P-diketone into the enol form, which is able to attack the protonated enone. The mechanistic detail is precisely analogous to the attack of an enolate the only difference is that both reactants are protonated. The product is the enol form of the triketone, which rapidly tautomerizes to the more stable keto form. 

Ninhydrin is a useful reagent for detecting amino acids and determining the concentrations of their solutions. It is the hydrate of a cyclic triketone, and when it reacts with an amino acid, a violet dye is produced. The overall reaction, whose mechanism is complex and need not concern us in detail here, is as follows ... 

More recently, Gryko reported an isolated example of a proline mediated cyclization of non-cyclic triketones.The reaction followed a domino Michael-Aldol pathway in the preparation of compound 29. The yields and % ee of these reactions are very solvent dependent and much lower than those reported for the Hajos-Wiechert reaction. Typically, the best results were obtained in NMP. 

Sodium carbonate 1,2,3-Triketones from / -diketones via 2-azo-, 2-amino-, 2-diazo-, and 2-hydroxy-1,3-diketones Cyclic trans-tixed -diketones Reduction of water-solubility... 

We investigated an interaction of 2-acyl( clohexane-l,3-diones la-c containing a perfluoroalkylated side chain with o-phenylenediamine. A direct reaction of the latter with o-phenylenediamine produees a mixture of acid cleavage products, as reported for their aeyelie analogues [7], As an alternative approach to the synthesis of perfluoroalkylated dibenzo[b,e][l,4]diazepinones, an interaction of enol ethers of 2-perfluoroalkanoylcyclohexane-l,3-diones la- c with o-phenylenediamine is proposed, beeause of an advanced reactivity of enol ethers to nucleophilic reagents versus the initial cyclic P,P -triketones [8],... 

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