Alkylation of 3-dicarbonyl compounds

The resulting anions are alkylated very efficiently. This diketone is enolized even by potassium carbonate, and reacts with methyl iodide in good yield. Carbonate is such a bad nucleophile that the base and the electrophile can be added in a single step. 

Among the [ -dicarbonyls, two compounds stand out in importance—diethyl (or dimethyl) mal-onate and ethyl acetoacetate. You should make sure you remember their structures and trivial names. 

With these two esters, the choice of base is important nucleophilic addition can occur at the ester carbonyl, which could lead to transesterification (with alkoxides), hydrolysis (with hydroxide), or amide formation (with amide anions). The best choice is usually an alkoxide Identical with the alkoxide component of the ester (that is, ethoxide for diethyl malonate methoxide for dimethyl malonate). Alkoxides (pKd 16) are basic enough to deprotonate between two carbonyl groups but, should substitution occur at C=0, there is no overall reaction. 

In this example the electrophile is the allylic cyclopentenyl chloride, and the base is ethoxide in ethanol—most conveniently made by adding one equivalent of sodium metal to dry ethanol. 

You met these fcampouncte ahdttifflr stable ends, in Chapter 

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Alkylation of (3-dicarbonyl compounds is highly regioselective for the a carbon flanked by two carbonyl groups. A proton at this carbon in a P-ketone is relatively acidic (p a 9) and is removed by bases even as weak as carbonate. 

Alkylation of P-dicarbonyl compounds and p-keto esters occurs preferentially on the carbon atom, whereas acylation produces the 0-acyl derivatives (see Chapter 3). There are indications that C- and 0-alkylated products are produced with simple haloalkanes and benzyl halides, but only C-alkylated derivatives are formed with propargyl and allyl halides [e.g. 90]. Di-C-alkylation frequently occurs and it has been reported that the use of tetra-alkylammonium 2-oxopyrrolidinyl salts are more effective catalysts (in place of aqueous sodium hydroxide and quaternary ammonium salt) for selective (-90%) mono-C-alkylation of p-dicarbonyl compounds [91]. 

Beside the Friedel-Crafts-type alkylation of arenes, the direct functionalization of 2,4-pentanediones is of great interest in Lewis acid catalysis. Although Pd-catalyzed Tsuji-Trost type allylations of 1,3-diketones are known, direct benzylation procedures catalyzed by Lewis acids are less explored [40-43]. Based on the previously described Friedel-Crafts alkylation of arenes and heteroarenes, the Rueping group developed a Bi(OTf)3-catalyzed benzylation of 2,4-pentanediones. Alcohols such as benzyl, allyl or cinnamyl alcohols were used as the electrophilic component to yield important 2-alkylated 1,3-dicarbonyl compounds. Initially, different Bi(III) salts were screened. In contrast... 

Apart from their fundamental role in sulfur ylide chemistry, sulfonium salts have found applications as soft electrophiles. In alkylation of ambident nucleophiles such as the enolates of [3-dicarbonyl compounds they led to selective C-alkylation [205],... 

Many alkylation and acylation reactions are most effective using anions of /3-dicarbonyl compounds that can be completely deprotonated and converted to their enolate ions by common bases such as alkoxide ions. The malonic ester synthesis and the acetoacetic ester synthesis use the enhanced acidity of the a protons in malonic ester and acetoacetic ester to accomplish alkylations and acylations that are difficult or impossible with simple esters. 

The parent ring system (53) was prepared by diazotization of 2-hydrazinopyrimidine (57JAP570777). Alkyl derivatives of (53) have been synthesized by the condensation of /3-dicarbonyl compounds with 5-aminotetrazole (79JCS(P1)3085). For example, treatment of 5-aminotetrazole with pentane-2,4-dione gave 5,7-dimethyltetrazolo[l,5-a]pyrimidine (Scheme 72) (65JOC826). 

Ambient nucleophiles ( S-diketones or jS-ketoesters) are known to attack always by the more basic y-carbon atom. A difficulty, frequently encountered in intramolecular alkylation of S-dicarbonyl compounds, is the concurrent formation of both C- and 0-alkylated products. It is, however, normally possible to direct the alkylation toward carbon or oxygen by proper selection of (1) the solvent, (2) the enolate counter ion, and (3) the leaving group. 

These doubly stabilized anions are alkylated so well that it is common to carry out an alkylation between two carbonyl groups, only to remove one of them at a later stage. This is made possible by the fact that carboxylic acids with a 3-carbonyl group decarboxylate (lose carbon dioxide) on heating. The mechanism below shows how. After alkylation of the dicarbonyl compound the unwanted ester is first hydrolysed in base. Acidification and heating lead to... 

Carbon atoms of C-H bonds adjacent to heteroatoms can be employed in C-C bond forming reactions with 1,3-dicaibonyl compounds (Scheme 4-255). Nonacarbonyl-diiron is applied in catalytic amounts in the presence of di-tert-butyl peroxide (DTBP) to afford alkylated 1,3-dicarbonyl compounds in moderate to good yields. When a mixture of two diastereoisomers is obtained in 1 1 to 2 1 ratios. ... 

Another possibility is that both nitrogen atoms react with a double alkylating agent. In this way fused pyrazole derivatives (pyrazolo[l,2-a]pyrazoles) like (237) can be obtained by reaction of 3,5-dimethylpyrazole with 1,3-dichloropropane or l-chloro-3-propanol (69BSF2064). More surprising is the reaction with a-chlorocarbonylphenylketene which yields the paraionic compound (238) (80JA3971) which can also be obtained from 3,5-dihydroxy-4-phenylpyrazole and /3-dicarbonyl compounds (82JOC295). 

Reaction of 1,3-dicarbonyl compounds with IVJV-dimethylformamide dimethyl acetal followed by malonamide in the presence of sodium hydride gives 5,6-disubstituted 1,2-dihydro-2-oxopyridine-3-carboxamides, whereas reaction of the intermediate enamines with cyanothioacetamide or cyanoacetamide in the presence of piperidine provides 2-thioxopyridine-3-carboxamides and 4,5-disubstituted l,2-dihydro-2-oxopyridine-3-carboxamides, respectively <95S923>. P-Enaminonitriles 14 react with p-ketoesters and alkyl malonates, in the presence of stoichiometric amounts of tin(IV) chloride, to afford 4-aminopyiidines 15 and 4-amino-2-pyridones 16 <95T(51)12277>. 

Alkylation of dianions occurs at the more basic carbon. This technique permits alkylation of 1,3-dicarbonyl compounds to be carried out cleanly at the less acidic position. Since, as discussed earlier, alkylation of the monoanion occurs at the carbon between the two carbonyl groups, the site of monoalkylation can be controlled by choice of the amount and nature of the base. A few examples of the formation and alkylation of dianions are collected in Scheme 1.7. In each case, alkylation occurs at the less stabilized anionic carbon. In Entry 3, the a-formyl substituent, which is removed after the alkylation, serves to direct the alkylation to the methyl-substituted carbon. Entry 6 is a step in the synthesis of artemisinin, an antimalarial component of a Chinese herbal medicine. The sulfoxide serves as an anion-stabilizing group and the dianion is alkylated at the less acidic a-position. Note that this reaction is also stereoselective for the trans isomer. The phenylsulfinyl group is removed reductively by aluminum. (See Section 5.6.2 for a discussion of this reaction.)... 

Several interesting reactions have been described for quinolizine-3-diazonium tetrafluoroborate 121. Thus, its treatment with secondary amines gave the corresponding triazenes 122 <2004ZNB380>, while its reaction with 1,3-dicarbonyl compounds gave the corresponding hydrazones. In the case of alkyl 4-chloro-3-oxobutanoates, the intermediate hydrazone 123 furnished a pyrazole derivative 124, as shown in Scheme 17 <2002H(57)2091>. 

Diazomalonic esters, in their behavior towards enol ethers, fit neither into the general reactivity pattern of 2-diazo-l,3-dicarbonyl compounds nor into that of alkyl diazoacetates. With the enol ethers in Scheme 17, no dihydrofurans are obtained as was the case with 2-diazo-l,3-dicarbonyl compounds. Rather, copper-induced cyclo-propanation yielding 70 occurs with ethoxymethylene cyclohexane u4). However,... 

Dicarbonyl compounds can be converted into furans by methods other than the classical Feist- Benary method, the essential feature of which is alkylation by a haloketone or similar species. A curious variation is provided by the use of trichloronitroethene, Cl2C=CCIN02, which condenses with two moles of a 1,3-dicarbonyl compound by Michael addition followed by elimination of two chloride ions the third chloride is lost at the aroma-tization step so that, for example, methyl 3-oxobenzenepropanoate is converted into the nitrofuran 38."... 

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... 

By treating the 1,3-dicarbonyl compound acety-lacetone with methyl iodide in the presence of potassium carbonate, one observes alkylation at the central carbon. 

When R2 substituent is flourocontaining alkyl group, the transformation 17 18 becomes hindered and its proceeding requires some special methods. For example, in [48] Biginelli-like cyclocondensations based on three-component treatment of 3-amino-l,2,4-triazole or 5-aminotetrazole with aldehydes and fluorinated 1,3-dicarbonyl compounds were investigated. It was shown that the reaction can directly lead to dihydroazolopyrimidines 20, but in the most cases intermediate tetrahydroderivatives 19 were obtained (Scheme 10). To carry out dehydration reaction, refluxing of tetrahydroderivatives 19 in toluene in the presence of p-TSA with removal of the liberated water by azeotropic distillation was used. The same situation was observed for the linear reaction proceeding via the formation of unsaturated esters 21. 

Alkylation reactions of dianions occur at the more basic carbon. This technique allows alkylation of 1,3-dicarbonyl compounds to be carried out cleanly at the less acidic position. Because, as discussed earlier, alkylation of the monoanion occurs at the carbon between the two carbonyl groups, the site of monoalkylation can be controlled by choice of the amount and nature of the base. A few examples of the formation and alkylation of dianions are collected in Scheme 1.8. 

On the basis of previous results, the Rueping group started to study alkylations with activated alkenes and nucleophiles other than arenes. Recently, Lewis- and Brpnsted-acid-catalyzed hydroalkylation procedures with 1,3-dicarbonyl compounds as nucleophiles have been developed [69, 70]. These reactions primarily utilized Pd... 

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