Keten intermediates in the uncatalysed alcoholysis of β-keto-esters and related compounds

Campbell, D. S.; Lawrie, C. W.

doi:10.1039/c29710000355

Cited by 28 publications

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“…This observation suggests that transesterification of β‐keto esters is facilitated by the electron‐withdrawing (EW) character of the carbonyl in geminal position to the ester group. The origin of the latter could be attributed to their enol character and the reaction was supposed to precede via an acetylketene intermediate , . Primary nitro compounds bearing an EW substituent in a geminal position, show similar tautomerism, (nitro – aci) as the acidity of the methylenic protons is enhanced , …”

Section: Resultsmentioning

confidence: 99%

Transesterification of Methyl 2‐Nitroacetate to Superior Esters

2020

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Methyl 2‐nitroacetate and methyl acetoacetate have in common the presence of an electron‐withdrawing substituent geminal to the methyl ester function but the well‐known ease of thermal transesterification of methyl acetoacetate has not been found in methyl 2‐nitroacetate. The latter gives uncatalysed thermal transesterification only in low yield and at a temperature higher than that of methyl acetoacetate. Comparative experiments provided further insight into the reactions; protic and Lewis acid catalysts promoted the smooth exchange of the alkanoyl groups, observing first the transesterification of methyl 2‐nitroacetate with ethanol, already proved difficult to proceed. Dibutyltin(IV)oxide (DBTO) catalyst offered the spur to set up a convenient synthetic methodology from methyl 2‐nitroacetate, encompassing higher molecular weight and functionalised alcohols: aliphatic, unsaturated and oxidation sensitive species were suited to react, delivering the corresponding 2‐nitroacetate esters in good yields in most cases.

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Section: Resultsmentioning

confidence: 99%

Transesterification of Methyl 2‐Nitroacetate to Superior Esters

2020

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“…Alternatively, the formation of an acylketene intermediate, as proposed by Lawrie and Campbell, may also occur (Scheme 1). 10 A broad range of viable reaction conditions has been developed for the transesterication of b-keto esters. 11,12 The kinetics of transesterications are typically slow, so a catalyst is normally required.…”

Section: Introductionmentioning

confidence: 99%

“…The catalyst is selective for b-keto esters and a-keto esters. The reaction likely proceeds by way of an acyl ketene intermediate as equimolar amounts of methyl acetoacetate and ethyl benzoylacetate afforded methyl benzoylacetate and ethyl acetoacetate respectively via exchange of the alcohol fragments of both b-keto esters 10.…”

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Recent advances in the transesterification of β-keto esters

Hennessy

O’Sullivan

2021

RSC Adv.

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“…The catalyst probably activates the b-keto esters to form an acyl ketene intermediate which is not feasible for the other esters as proposed by Campbell and Lawrie [20]. In order to further prove the reaction mechanism, we carried out another set of reaction between two different b-ketoesters as suggested by the referees.…”

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Al(H2PO4)3: An Efficient and Effective Solid Acid Catalyst for Transesterification of β-keto Esters Under Solvent Free Condition

Goswami

Bharadwaj

2008

Catal Lett

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Al(H 2 PO 4 ) 3 is an efficient, cheap and reusable heterogeneous catalyst for transesterification of b-ketoesters with a variety of alcohols in moderate to good yields within a short reaction time under solvent free condition.Keywords b-keto esters Á Alcohols Á Transesterification Á Solid catalyst Á Catalytic synthetic protocolThe transesterification of b-keto esters is an important transformation in organic synthesis as they are precursors of many important chemical intermediates, agrochemicals, polymer as well as in pharmaceutical industries [1]. The transesterification strategy is also employed for preparing optically active compounds from b-ketoesters by reaction with chiral alcohols [2]. Conventionally, dimethylamino pyridine (DMAP) is used as a choice of reagent for transesterification of b-keto esters in good yields, but it suffers from the limitations such as toxicity, high price and requirement of large amount of catalyst [3]. Over the years several catalysts like distannoxane [4], triphenyl phosphine [5], zeolites [6], kaolinitic clay [7], Zn/I 2 [8], ceria-yttria based Lewis acid catalyst [9], Nb 2 O 5 [10], 3-nitrobenzeneboronic acid [11] have been reported to accelerate the rate of transesterification of b-keto esters. Similarly some other heterogeneous catalysts such as S-SnO 2 [12], Amberlyst-15 [13], Envirocat EPZF R [14], montmorillonite K-10 [15], B 2 O 3 /ZrO 2 [16] are also effective for the transesterification of b-ketoesters. Nevertheless, there is still an ample scope to search for an effective catalyst for transesterification as most of the methods suffer from drawbacks such as longer reaction time, tedious work-up procedure, harsh reaction conditions and expensive reagents.Recently, there has been a considerable interest to develop catalysts for organic reactions by supporting inorganic reagents on inorganic materials having high surface area [17]. The nature of support has an important role in the catalytic activity mainly due to the intimate contact between the supported ions and the support surface. Moreover, the mechanical stability, ease of separation of catalyst from the reaction mixture and reusability are the added advantages of these solid catalysts.We wish to report herein the transesterification of b-ketoesters with a wide range of alcohols by using 5 mol% of solid acid catalyst Al(H 2 PO 4 ) 3 under solvent free condition within a very short reaction time (Scheme 1).Al(H 2 PO 4 ) 3 is a solid acid catalyst which is easy to prepare, stable, easily separable from the reaction mixture and recyclable which was prepared by literature procedure [18]. For optimization, the reaction of methyl acetoacetate with benzyl alcohol was carried out at various conditions and the results are summarized in Table 1. A blank reaction of methyl acetoacetate (5 mmol) and benzyl alcohol (5.5 mol) without using the catalyst was carried out which gave only 15% of the desired b-keto ester even after stirring for 24 h at room temperature. The same reaction in presence of Al(H 2 PO 4 ) 3 (0.5 mol%) at ro...

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Keten intermediates in the uncatalysed alcoholysis of β-keto-esters and related compounds

Abstract: Uncatalysed alcoholysis of alkyl acetoacetates and malonates occurs via a unimolecular dissociative mechanism involving concerted elimination of alcohol with resultant formation of substituted ketens as reactive intermediates.

Cited by 28 publications

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Transesterification of Methyl 2‐Nitroacetate to Superior Esters

Transesterification of Methyl 2‐Nitroacetate to Superior Esters

Recent advances in the transesterification of β-keto esters

Al(H2PO4)3: An Efficient and Effective Solid Acid Catalyst for Transesterification of β-keto Esters Under Solvent Free Condition

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