L diketones

In the 1880s, Pinner found that the amidine derivative 2 reacted with acetoacetic ester (4) to furnish 2-substituted-6-hydroxy-4-methylpyrimidine 5. The condensation of amidine derivative 2 with other (l-keto esters, malonic esters, and (l-diketones proceeded similarly (see the following pages for examples). ... 

Structure and bonding in inorganic derivatives of (l-diketones. D. W. Thompson, Struct. Bonding (Berlin), 1971,9,27-47 (69). 

Example 13 The extraction of Zn(II) by (l-diketones and phosphoryl adduct formers (cont. of Example 5). 

Fig. 6 Enzymatic splitting of the oxidised polymer backbone proceeds by two different enzymes depending on the target moiety in the oxidised polymer backbone. Above, the [1-OH-ketone can be opened by an aldolase activity (apoenzyme of PVADH). Below, the diketone element is cleaved by a specific [l-diketone hydrolase (BDH). A non-enzymatic mechanism is also possible...

Sakai K, Hamada N, Watanabe Y (1986) Degradation mechanism of poly(vinyl alcohol) by successive reactions of secondary alcohol oxidase and [l-diketone hydrolase from Pseudomonas sp. Agric Biol Chem 50 989-996... 

Several complexes with Schiff bases derived from the reaction of /l-diketones and diamines (67) have been prepared and many publications on them have appeared.523,725 743-748 Almost all are monomeric (no V - V interactions) and five-coordinate square pyramidal, as in (67). This structure has been confirmed in [VO(acen)] (acen = 67 R1 = R2 = Me, R = X = H). 

Y. Lin and C. M. Wai, Supercritical Fluid Extraction of Lanthanides with Fluorinated (L Diketones and Tributyl Phosphate, Anal. Chem. 1994,66, 1971. 

Other workers have concurrently developed the extensive acid-base chemistry of palladium and platinum /l-diketonates.44 452 Sequential displacement reactions also occur with Pt(CF3COCHC-OCF3)2, Pt(CF3COCHCOMe)2 and Pd(CF3COCHCOMe)2. Pdtetrakis(aniline)2+ diketonates are... 

Fig. 42. (Left) Partial luminescence quantum yields (4F3/2 4In/2 transition) of Nd111 tris(/l-diketonates).

The net effect of the Stork enamine sequence is the Michael addition of a ketone to an o, unsaturatcd cprbonyl compound. For example, cyclohexanone reacts with the cyclic amine pyrrolidine to yield an enamine fuj-ther reaction with an enone ssich as 3-buten-2 One yields a Michaahtyi>e adduct and aqueous hydrolysie completes the sequence to provide a l/> diketone product (Figure 23.8>. 

Figure 2.28 An ORTEP view of the crystal structure of Eu(L )3(TPTZ) with partial atomic labeling. Thermal ellipsoids are drawn at the 50% probability level [25]. (Reprinted from Polyhedron, 26, C.R. De Silvaa, J.R. Maeyera, A. Dawsona and Z. Zheng, Adducts of lanthanide [l-diketonates with 2,4,6-tri(2-pyridyl)-l,3,5-triazine synthesis, structural characterization, and photoluminescence studies, 1229-1238, 2007, with permission from Elsevier.)...

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 (l-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 involves acid-catalysed conversion of the keto form of the cyclic (l-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 shown above the only difference is that both reactants are... 

When a hydr< en atom is flanked by two carbonyl groups, its aodif is enhanced even more. Table 22.1 thus shows that compounds such as diketones (/l diketones), 3-oxo esters (p-keto esters), and 1,3-diesters are more acidic than water. This enhanced acidity of /3-dicarbonyI compounds is due to the fact that the resultant enolate ions are stabilized by delocalization of the negative charge over two carbonyl groups. Hie enolate ion of 2,4-pentanedione, for example, has three resonance forms. Similar resonance forms can be drawn for other doubly stabilized enolate ions. 

Thompson, D. W. Structure and Bonding in Inorganic Derivatives of (l-Diketones. Vol. 9,... 

Emsley E (1984) The Composition, Structure and Hydrogen Bonding of the /l-Diketones. 57 147-191... 

Since 1,5-enediones are usually obtained via pyrylium salts, syntheses of the type found in Section B, 2, a have a rather theroetical interest, save for a few special syntheses. There exist several direct syntheses of 1,5-enediones, e.g., from /3-chlorovinyl ketones and /l-diketones or j8-keto esters222,223 special pathways to 1,5-enediones have also been described, namely, oxidation with lead tetraacetate or with periodic acid of cyclopentene-l,2-diols.219,220,221... 

Intermolecular de Mayo reactions are efficient for cyclic 1,3-diketones such as dimedone (5,5-dimethyl-l,3-cyclohexanedione)96,103,104 and acyclic systems such as acetylacetone93-95. Unsymmetrical acyclic /l-diketones, such as 1-phenyl-1,3-butanedione98 can enolize in two directions, however, reaction normally occurs preferentially from a single enol form. Examples of alkene photocycloaddition to trapped ends of /(-dicarbonyl compounds (e.g., 2,2-dimethyl-3(2/f)-furanone and 2,2.6-trimethyl-4/f-l,3-dioxin-4-one) are given in Table 1 (entries 26, 27) and Table 2 (entry 35) 10°. If the enol is stabilized by derivatization (e.g., acetylated dimedone 3-acetoxy-5,5-dimethyl-2-cyclohexenone), the primary cyclobutane photoproducts can be isolated96. 

It is necessary to note that later on we elaborated an alternative, shorter route for preparation of the hydroxy ketone (63) from the sclareol (3) [47] (Scheme 10). On the ozonolysis of the sclareol (3) and subsequent treatment of the ozonolysis products with ammonium chloride, the dimeric product (70) is formed [48]. Its further ozonolysis gave the (l-diketone (71). 

Oxy-4. . diiDSthoxy-cbslkon 8 II482. [4-Methoxy. edyl]-[4.methoxy-ben l]-diketon 8 II 482. 

Tang S, Mudring AV (2009) Terbium (l-diketonate based highly luminescent soft materials. Eur J Inorg Chem 2769-2775... 

---