Enolates Of 1,3-Dicarbonyls

As the dinucleophilic reagent, sodium enolates of 1,3-dicarbonyl compounds can be used. When dinitropyridone 1 is treated with sodium enolate 13b derived from diethyl 3-oxopentanedioate, the RTF reaction proceeds to give 2,6-bis(ethoxycarbonyl)-4-nitrophenol 14b in 91% yield [39]. Enolates of ethyl 3-oxobutanoate 13a and 2,4-pentadione 13c similarly react to give corresponding functionalized 4-nitrophenols 14a and 14c, respectively. 

Enols of 1,3-dicarbonyl compounds thermodynamically stable enols... 

Ambident anions are mesomeric, nucleophilic anions which have at least two reactive centers with a substantial fraction of the negative charge distributed over these cen-ters ) ). Such ambident anions are capable of forming two types of products in nucleophilic substitution reactions with electrophilic reactants . Examples of this kind of anion are the enolates of 1,3-dicarbonyl compounds, phenolate, cyanide, thiocyanide, and nitrite ions, the anions of nitro compounds, oximes, amides, the anions of heterocyclic aromatic compounds e.g. pyrrole, hydroxypyridines, hydroxypyrimidines) and others cf. Fig. 5-17. 

Lactone annelatlon. Enolates of 1,3-dicarbonyl compounds undergo 1,6-Michael addition to 1 subsequent cyclization results in lactone annelation (equation... 

These last reagents, where the anion is stabilized both by the adjacent carbonyl group (as an enolate) and by the adjacent P=0 group, are just one of many examples of enolate anions stabilized by two electron-withdrawing groups. The most important members of this class, enolates of 1,3-dicarbonyl compounds, are the subject of the next section. 

As an alternative procedure (type 2 reaction), coupling of the o-ethynylphenol 80 with the alkenyl triflate 81 proceeds smoothly to yield the benzofuran 82 [40]. Coupling of 2-bromothiazole with an enolate of 1,3-dicarbonyl compound was used for preparation of 2,5-disubstituted furan 83 [47]. Coupling of 2-iodoanisole... 

Formation o( oleltns by coupling or cross coupling of ketones, mediated by low valent titanium Also coupling ol enol ethers of 1,3-dicarbonyl compounds. 

Treatment of 1,3-dicarbonyl eompounds with two equivalents of strong base ean give a dianion that will react selectively with alkyl halides. For example, ethyl acetoacetate reacts first with NaH to form an enolate, and then with n-BuLi to form a dianion. This then adds t-PrI. 

Given the large number of tandem cyclization processes that have been explored [63], it is disappointing to note that so few have been promoted electrochemi-cally. There appears to be a significant opportunity for additional exploration. Two tyiws of tandem cathodic cyclizations are discussed below. The first involves generation of a ketyl, and its subsequent cyclization onto a pendant alkene to afford a new radical that closes onto a second alkene [64,65]. The second focuses on chemistry not yet discussed involving the reductive cyclization of enol phosphates of 1,3-dicarbonyl compounds [66]. 

The reductive cyclization of readily available enol phosphates of 1,3-dicarbonyl compounds bearing pendant olefinic units has been explored [66,67]. The chemistry is exceptionally interesting, and provides a unique route to structures possessing a cyclopropyl unit which is suitable for structural elaboration. The reaction occurs in a manner wherein the phosphate-bearing carbon behaves like a carbene that adds to the pendant alkene to form a cyclopropane. While this provides a useful way of viewing the transformation, mechanistic studies indicate that a carbene is not an actual intermediate. Examples are portrayed in Table 11. 

Peroxidases catalyze not only the formation of halohydrines, but also the halo-genation of 1,3-dicarbonyl compounds. In CPO-catalyzed halogenation of eno-lizable substrates, the halonium ion is trapped by the enolate to afford the corresponding mono- and dihalogenated products (Eq. 9, Table 10). 

During the coverage period of this chapter, reviews have appeared on the following topics reactions of electrophiles with polyfluorinated alkenes, the mechanisms of intramolecular hydroacylation and hydrosilylation, Prins reaction (reviewed and redefined), synthesis of esters of /3-amino acids by Michael addition of amines and metal amides to esters of a,/3-unsaturated carboxylic acids," the 1,4-addition of benzotriazole-stabilized carbanions to Michael acceptors, control of asymmetry in Michael additions via the use of nucleophiles bearing chiral centres, a-unsaturated systems with the chirality at the y-position, and the presence of chiral ligands or other chiral mediators, syntheses of carbo- and hetero-cyclic compounds via Michael addition of enolates and activated phenols, respectively, to o ,jS-unsaturated nitriles, and transition metal catalysis of the Michael addition of 1,3-dicarbonyl compounds. ... 

A mechanistic study of acetophenone keto-enol tautomerism has been reported, and intramolecular and external factors determining the enol-enol equilibria in the cw-enol forms of 1,3-dicarbonyl compounds have been analysed. The effects of substituents, solvents, concentration, and temperature on the tautomerization of ethyl 3-oxobutyrate and its 2-alkyl derivatives have been studied, and the keto-enol tautomerism of mono-substituted phenylpyruvic acids has been investigated. Equilibrium constants have been measured for the keto-enol tautomers of 2-, 3- and 4-phenylacetylpyridines in aqueous solution. A procedure has been developed for the acylation of phosphoryl- and thiophosphoryl-acetonitriles under phase-transfer catalysis conditions, and the keto-enol tautomerism of the resulting phosphoryl(thiophosphoryl)-substituted acylacetonitriles has been studied. The equilibrium (388) (389) has been catalysed by acid, base and by iron(III). Whereas... 

Dicarbonyl compounds are widely used in organic synthesis as activated nucleophiles. Because of the relatively high acidity of the methylenic C—H of 1,3-dicarbonyl compounds, most reactions involving 1,3-dicarbonyl compounds are considered to be nucleophilic additions or substitutions of enolates. However, some experimental evidence showed that 1,3-dicarbonyl compounds could react via C—H activations. Although this concept is still controversial, it opens a novel idea to consider the reactions of activated C H bonds. The chiral bifunctional Ru catalysts were used in enantioselective C C bonds formation by Michael addition of 1,3-dicarbonyl compounds with high yields and enantiomeric excesses. ... 

The nucleophilic core of 4-hydroxycoumarin (Scheme 18) represents the enolic form of 1,3-dicarbonyl functionality, which was efficiently alkylated with a low amount of Bi(OTf)3 (Schemes 11 and 12). Therefore, Rueping et al. investigated a Bi(OTf)3-catalyzed benzylation of 4-hydroxycoumarins [52],... 

Enol Ethers and Esters 0-15 O-Alkylation of carbonyl compounds with diazo alkanes 0-17 Transetherification 0-20 Reaction between acyl halides and active hydrogen compounds 0-23 Transesterification 0-24 Acylation of vinylic halides 0-94 Alkylation with ortho esters 0-107 O-Acylation of 1,3-dicarbonyl compounds... 

Protected 1 -dicarbonyl compounds.5 Use of ZnCl2 as catalyst promotes the reaction of enol silyl ethers with 2-ethoxy-l,3-dithiolane (1) to give the protected derivative (2) of 1,3-dicarbonyl compounds. 

Cyclic vinyl-A3-iodanes undergo direct a-vinylations of 1,3-dicarbonyl compounds [132]. In these reactions, the desired a-vinylations were accompanied by a-arylations as a competing side reaction thus, reaction of the potassium enolate of 2-methyl-1,3-indandione to cyclohexenyl(phenyl)-A3-iodane 22a afforded 2-cyclohexenyl-l,3-indandione in 86 % yield and 2-phenyl-1,3-indandione in... 

We need first of all to convert the ketone 39 completely into some enolate derivative so that there is no ketone left for self-condensation. In this chapter we shall restrict ourselves to lithium enolates 40 and anions 42 of 1,3-dicarbonyl compounds 41. Each of these reagents acts as the enolate anion of acetone 38 R2 = Me. 

Manganese acetate-promoted oxidative addition of 1,3-dicarbonyl compounds (351) to endo-cyclic enol ethers (352) and enol lactones (353) gives 2,3,3a,6a-tetrahydrofuro[2,3-6]furan derivatives (354) and (355) <87CL223, 91TL711, 91TL7107). 

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