Ketones with esters

An extension of this synthesis would be the condensation of -keto esters with ketones leading to alkoxypyrylium salts and hence to 2- or 4-pyrones however, attempts at such reactions were unsuccessful. ... 

The condensation of esters with ketones proceeds in an exactly similar way the enol-form of the ketone (in the form of a salt) is the basis of the addition, e.g. 

Darzens condensation. Hinckley found that the condensation of a-halo esters with ketones when effected with sodium hydride dispersion proceeds smoothly and without usual side reactions. 

As mentioned above, / -diketones can be obtained by condensation of esters with ketones, but they can also be prepared in another way, namely, by reaction of methyl ketones with acid anhydrides in the presence of boron... 

Diketones. The reaction of enol esters with ketones at 50-70° in the presence of manganic acetate (2 eq.) leads to 1,4-diketones in moderate yields ... 

Cobalt octoate/dimethyl aniline liquid mixture in phthalate Special for bisphenol A or vinyl esters with ketone peroxides or peresters short gel/cure times 10-100 C a bed EG... 

Frequently, the strong base sodamide (NaNH2) or LDA is used in condensing esters with ketones. These conditions favor removal of the kinetically more accessible hydrogen when there is a choice of possible enolates (Fig. 19.96). 

Scheme 10.20 Reformatsky reaction of an a-bromo ester with ketones.

Treatment of a-silyl esters with a base readily affords the corresponding enolates, which can be utilized for Peterson reactions (Scheme 2.70) [189-196]. LDA is the most widely used base for the deprotonation of a-silyl esters. The carbonyl compounds used in the above reactions are aldehydes, saturated and unsaturated ketones, amides, lactones, and lactams. The products, a,j8-unsaturated esters, are obtained as mixtures of the E- and Z-isomers in most cases. When another trimeth-ylsilyl group is present on the anionic carbon atom, the reactions of the carban-ion derived from the a,a-bis(trimethylsilyl) esters with ketones are unsuccessful, probably because of steric reasons, and result only in enolization [197]. 

W. Wang, M.-H. Xu, X.-S. Lei, G.-Q. Hn, Chiral sulfonamide induced enantioselective protonation of samarium enolate in the reaction of a,p-unsaturated ester with ketone, Org. Lett. 2 (2000) 3773-3776. 

Scheme 3.34 Epoxidation of silyl enol ethers and esters with ketone 39 [49, 50]...

Scheme 3.43 Epoxidation of a,P-unsaturated esters with ketone 56 (0.2-0.3 equiv.)...

Claisen condensation Condensation of an ester with another ester, a ketone or a nitrile in the presence of sodium ethoxide, sodium or sodamidc, with the elimination of an alcohol. The result is the formation of a / -ketonic ester, ketone, or nitrile respectively, e.g. 

C HgNjOjS. Colourless needles, with iH20. Prepared by reducing diazotized sulphanilic acid with an excess of sodium sulphite. It is a typical hydrazine in its reactions with ketones, and with acetoacetic ester. The latter reaction gives rise to the tartrazine dyestuffs, and is much used commercially. 

Thus the sodio derivative (I) of the enol form of ethyl acetoacetate is obtained. This mechanism can clearly apply also to the condensation of an ester with a suitable ketone or nitrile, as in the above reactions (ii) and (iii) respectively. 

The reaction with sodium is by no means an infallible practical test for alcohols since, strictly speaking, it is applicable only to pure anhydrous liquids. Traces of water, present as impurities, would give an initial evolution of hydrogen, but reaction would stop after a time if an alcohol is absent furthermore, certain esters and ketones also evolve hydrogen when treated with sodium (compare Section XI,7,6). It may, however, be assumed that if no hydrogen is evolved in the test, the substance is not an alcohol. 

Ketonic hydrolysis to di-iso-propyl ketone. Mix 15 g. of the ester with 30 ml. of glacial acetic acid, 10 ml. of water and 10 ml. of concentrated sulphuric acid, and reflux in a flask coimected by a ground glass joint... 

The reductive coupling of aldehydes or ketones with 01, -unsaturated carboxylic esters by > 2 mol samarium(II) iodide (J.A. Soderquist, 1991) provides a convenient route to y-lactones (K. Otsubo, 1986). Intramolecular coupling of this type may produce trans-2-hy-droxycycloalkaneacetic esters with high stereoselectivity, if the educt is an ( )-isomer (E.J. Enholm, 1989 A, B). 

No intennolecular reaction of malonate or /3-keto esters with halides has been reported, but the intramolecular reaction of /3-diketones such as 790 and malonates proceeds smoothly[652,653]. Even the simple ketone 791 can be arylated or alkenylated intramolecularly. In this reaction, slow addition of a base is important to prevent alkyne formation from the vinyl iodide by elim-ination[654]. 

Esters of nonenolizable monocarboxylic acids such as ethyl benzoate give p diketones on reaction with ketone enolates... 

The limitations of this reagent are several. It caimot be used to replace a single unactivated halogen atom with the exception of the chloromethyl ether (eq. 5) to form difluoromethyl fluoromethyl ether [461 -63-2]. It also caimot be used to replace a halogen attached to a carbon—carbon double bond. Fluorination of functional group compounds, eg, esters, sulfides, ketones, acids, and aldehydes, produces decomposition products caused by scission of the carbon chains. 

Reactions. The chemical properties of cyanoacetates ate quite similar to those of the malonates. The carbonyl activity of the ester function is increased by the cyano group s tendency to withdraw electrons. Therefore, amidation with ammonia [7664-41-7] to cyanoacetamide [107-91-5] (55) or with urea to cyanoacetylurea [448-98-2] (56) proceeds very easily. An interesting reaction of cyanoacetic acid is the Knoevenagel condensation with aldehydes followed by decarboxylation which leads to substituted acrylonitriles (57) such as (29), or with ketones followed by decarboxylation with a shift of the double bond to give P,y-unsaturated nitriles (58) such as (30) when cyclohexanone [108-94-1] is used. 

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