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A i-ketoesters

Substantial MW rate enhancements have been reported in the Biginelli synthesis of dihydropyrimidines [50, 51] under homogeneous conditions. The synthesis involves a one-pot cyclocondensation of a /i-ketoester with an aryl aldehyde and urea or thiourea in the presence of a catalytic amount of HC1 in ethanol solution. An example of this synthesis is shown in Scheme 4.17. [Pg.128]

This acid-catalyzed, three-component reaction between an aldehyde, a i-ketoester and urea constitutes a rapid and facile synthesis of dihydropyrimidones, which are interesting compounds with a potential for pharmaceutical application. [Pg.62]

In a Claisen condensation the carbanion-enolate of an ester adds to the C=0 group of its parent ester. The addition is followed by loss of the OR group of the ester to give a /i-ketoester. In a mixed Claisen condensation the carbanion-enolate adds to the C=0 group of a molecule other than its parent. [Pg.394]

The Carroll reaction occurs when a /i-ketoester is treated with an allylic alcohol in the presence of base, or when an allyl ester of a / -ketoacid is heated. Scheme 4.6 shows the mechanism of the latter. [Pg.59]

Of the two anionic carbon atoms, the terminal one (13C) is the more basic and therefore the stronger nucleophile because the charge is stabilized by only one adjacent carbonyl group. The remainder of the sequence is the completion of a (i-ketoester ketone synthesis. [Pg.453]

Notably, the use of liquid polymers in multiphase catalysis with SCCO2 is not restricted to transition metal catalysts. Biocatalysts can also be used in this environment, as demonstrated by the yeast-catalyzed reduction of a (i-ketoester that gave excellent (99%) enantioselectivity in PMPS-710 and the ionic liquid [P(Me)(Bu)3][ Bu)3][03SCgH4pMe] [Eq. (8)]. The product was isolated by extraction with water or SCCO2, respectively [54]. [Pg.685]

As an extension of this work, a total synthesis of sulfobacin A, a von Willebrand factor receptor antagonist, was reported by the same group, in 2004. The key steps of this short route to sulfobacin A involved ruthenium-catalysed asymmetric hydrogenation reactions of a /i-ketoester and a /J-keto-a-amino ester hydrochloride to afford, respectively, the corresponding enantiomerically pure S-hydroxy ester and the enantio-enriched anti -hydroxy-a-amino ester hydrochloride through DKRs (Scheme 2.15). [Pg.58]

In 2009, Feng and coworkers developed new guanidine catalysts with an amino amide skeleton [139]. Among the various catalysts tested, guanidine 49 was found to be the most active for the enantioselective Michael reaction of a (i-ketoester with nitroolefins (Scheme 10.46). The conjugate addition products were obtained in high yields and excellent diastereo- and enantioselectivities. The same researchers used bis-guanidine catalysts for the enantioselective inverse-electron-demand hetero-Diels-Alder reaction of chalcones with azlactones (Scheme 10.47) [140] and enantioselective Mannich-type reaction of a-isothiocyanato imide and sulfonyl imines (Scheme 10.48) [141]. [Pg.272]

The alkylation reactions of enolate anions of both ketones and esters have been extensively utilized in synthesis. Both very stable enolates, such as those derived from (i-ketoesters, / -diketones, and malonate esters, as well as less stable enolates of monofunctional ketones, esters, nitriles, etc., are reactive. Many aspects of the relationships between reactivity, stereochemistry, and mechanism have been clarified. A starting point for the discussion of these reactions is the structure of the enolates. Because of the delocalized nature of enolates, an electrophile can attack either at oxygen or at carbon. [Pg.435]

In a dedicated combinatorial approach, Strohmeier and Kappe have reported the rapid parallel synthesis of polymer-bound enones [33]. This approach involved a two-step protocol utilizing initial high-speed acetoacetylation of Wang resin with a selection of common /i-ketoesters (Scheme 7.13) and subsequent microwave-mediated Knoevenagel condensations with a set of 13 different aldehydes (see Section 7.3.6). [Pg.304]

A method for microwave-assisted transesterifications has been described by Van-den Eynde and Rutot [73], The authors investigated the microwave-mediated deriva-tization of poly(styrene-co-allyl alcohol) as a key step in the polymer-assisted synthesis of heterocycles. Several /i-ketoesters were employed in this procedure and multigram quantities of products were obtained when neat mixtures of the reagents in open vessels were subjected to microwave irradiation utilizing a domestic micro-wave oven (Scheme 7.65). The successful derivatization of the polymer was confirmed by IR, 1H NMR, and 13C NMR spectroscopic analyses. The soluble supports... [Pg.339]

There are only few examples of organic reactions catalysed effectively by Lewis acids which can be carried out in pure water without any organic co-solvent. While water can be used successfully for the uncatalysed Michael addition of 1,3-diketones (Table 4, entry D)22, the corresponding reaction of /i-kctocsters does not give satisfactory results. On the other hand, the Yb(OTf)3 catalysed Michael reaction of various /i-ketoesters (Table 21, entry A)257 and a-nitroesters (Table 21, entry B)258 takes place. [Pg.1073]

Alkylation of enolate is an important synthetic method.27 The alkylation of relatively acidic compounds such as /i-dikctoncs, /i-ketoesters, and esters of malonic acid can be carried out in alcohols as solvents using metal alkoxides as bases. The presence of two electron-withdrawing substituents facilitates formation of the enolate resulting from removal of a proton from the carbon situated between them. Alkylation then occurs by an Sn2 process. Some examples of alkylation reactions involving relatively acidic carbon acids are shown in Scheme 1.5. These reactions are all mechanistically similar in that a... [Pg.11]

Ketones are converted to /i-ketoesters by acylation with diethyl carbonate or diethyl oxalate, as illustrated by entries 5 and 6 in Scheme 2.15. Alkyl cyanoformate can be used as the acylating reagent under conditions where a ketone enolate has been formed under kinetic control.128 129 130 131... [Pg.109]

TA NaBr-MRNi has been found to be an effective catalyst for enantio-differentiating hydrogenations of ketones which have a general structure of R—CO—CH2—X—O— as shown in Table XVII (52c) and methyl ketones as shown in Table XXVI (52d). Among all, /i-diketones and /i-ketoesters are the most favorable substrate for this catalyst. Specific rotations [a] 0 of (R, R )-diols produced from /3-diketones by hydrogenation with this catalyst are summarized in Table XXVII (44). [Pg.266]

When an a-chloroaldehyde or an a-chloroketone is condensed with a /3-ketoester, in the presence of aqueous base, a furan is produced bearing an ester substituent at the /3-position. It is thought that the reaction is of the aldol type intermediate dihydrofurans (256) have been isolated in certain cases (Scheme 70) (74BSF519). The condensation of ethyl bromopyru-vate and sodium oxaloacetate follows a similar mechanism (54JOC1671). The one-pot synthesis of 2,4,5-trisubstituted furans (257) from ketones and ethyl 3,4-dibromo-2-butenoate is a useful addition to a well known route (80S52). The analogous reaction of cyclic /3-diketones, i.e. cyclohexane-1,3-dione and 5,5-dimethylcyclohexane-l,3-dione, results in the formation of the condensed furans (258) and (259). These reactions are preformed either in ethanol with sodium ethoxide or in DMF with potassium carbonate. [Pg.685]

A few natural products which contain the cyclopropyl ring have been synthesized through metal catalysed cyclopropanation using dicarbonyl diazomethanes. ( )-Cycloeudesmol 63, isolated from marine alga Chondria oppositiclada, was synthesized via a sequence involving a copper catalysed cyclopropanation of a-diazo-/8-ketoester 61 to give the key intermediate 62 (equation 73)1 7,108. Similarly, the bicyclo[3.1.0]hexane derivative 65 was synthesized from the corresponding a-diazo-/8-ketoester 64 via the catalytic method and was converted into ( )-trinoranastreptene 66 (equation 74)109. Intramolecular cyclopropanation of -diazo-/i-ketoesters 67 results in lactones 68 which are precursors to 1-aminocyclopropane-l-carboxylic acids 69 (equation 75)110. [Pg.677]

And finally, acylating agents can also be used as electrophiles to react with enamines. Following the hydrolysis of the enaminoketones (i.e., compounds with the substructure R2N-C=C-C(=0)-R ) or enaminoesters (i.e., compounds with the substructure R2N-C=C-C(=0)-0R ) the acylation products of the corresponding ketones are obtained. Figure 12.21 gives the mechanistic details of the acylation with an acid chloride, and Figure 12.22 shows the acylation with ethyl chloroformate. The first acylation yields /1-diketones, the second furnishes a /1-ketoester. [Pg.510]

Scheme 2.23. Domino Michael/aldol reaction of a,p-unsaturated ketones with (i-ketoesters. Scheme 2.23. Domino Michael/aldol reaction of a,p-unsaturated ketones with (i-ketoesters.
Some support for the 1,2,3-arrangement of substituents in the decalin nucleus was found in the behavior of the C-13 ketone (XIV) which gave a negative Zimmermann test and failed to yield a piperonylidene derivative it therefore did not contain an unhindered active methylene group. Also since the ketolactone XVIII gave a negative ferric test it was not a /3-ketoester i.e., it had structure XVIII rather than XIX. [Pg.539]

The sulfuration of /i-ketoesters with phosphorus pentasulfide alone or in a mixture with elemental sulfur is a general method for the synthesis of l,2-dithiole-3-thiones.4 Functional groups are introduced by means of fi-ketoesters substituted with such groups. In this way l,2-dithiole-3-thiones substituted with chloro, cyano, and ester groups in the 4-position5 5 and ester groups in the 5-position have been prepared56 (Scheme 1). [Pg.70]


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See also in sourсe #XX -- [ Pg.72 ]




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