Darzens glycidic ester condensation of benzaldehyde in solid-liquid two-phase system

Kimura, Chikai; Kashiwaya, Kageaki; Murai, Koichi; Katada, H.

doi:10.1021/i300009a026

Cited by 7 publications

(1 citation statement)

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“…However, with respect to α,β‐epoxy esters, their preparation by means of Darzens reactions remains far from ideal. Indeed, as far as α‐halo esters are concerned, hydrolysis of the trans epoxy esters has been reported, [35] even in the case of tert ‐butyl esters [36] . This reactivity has been invoked as a possible explanation for the low yields or the exclusive cis ‐selectivity observed in some cases [24b] .…”

Section: Introductionmentioning

confidence: 99%

Highly Efficient Darzens Reactions Mediated by Phosphazene Bases under Mild Conditions

2022

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The highly basic and poorly nucleophilic phosphazene base P 1t-Bu promotes the Darzens condensation of α-halo esters with aromatic aldehydes affording α,β-epoxy esters in nearly quantitative yields under mild conditions and in short reaction times. The more basic P 4 -t-Bu phosphazene was found useful with low reactivity aldehydes. These reactions can be performed in aprotic organic solvents of low polarity, thus minimizing the hydrolysis of α,β-epoxy esters which often accompanies the base-promoted Darzens condensations.

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Section: Introductionmentioning

confidence: 99%

Highly Efficient Darzens Reactions Mediated by Phosphazene Bases under Mild Conditions

2022

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Darzens Condensation

2010

Comprehensive Organic Name Reactions and Reagents

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The synthesis of glycidic esters from the condensation between aldehydes or ketones and esters of α‐halo‐carboxylic acids is known as Darzens condensation. This type of condensation has also been extended to α‐halogenated nitriles, sulfoxides, sulfones, sulfoximines, carboxylic amides, etc. The reaction between carbonyl compounds and α‐halogenated ketimine is also referred to as the aza ‐Darzens reaction. This reaction has been modified to occur in the solid‐liquid two‐phase system using a solid base and catalyst at temperatures higher than 100°C.

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Z/E ratios in Darzens Reactions and Cyclopropanations: Influence of phase transfer catalyst structure

Dehmlow

Kinnius

1995

J. Prakt. Chem.

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Systematic structure variation of catalysts has revealed that chemo-and regioselectivity of several phase transfer reactions can be influenced strongly by catalyst structure.Whereas typical quaternary ammonium and phosphonium ions show little selectivity control, there are two groups of catalysts with opposite steering effects:(1) Small and sterically unencumbered ammonium salts as well as some benzo-crown ethers, (2) sterically hindered and large catalyst as well as highly delocalized cations. Rather spectacular effects are found, for example, in the following reactions ((a) to (c); Scheme (a) NMe4CI and dibenzo-18-crown-6 catalyzed 97-99 % selectivity for A, AsPh4Br gives a 52 : 40 : 8 mixture of A, B, (b) "Cetrimid (hexadecyltrimethylammonium bromide) leads to a D/(E + F) ratio of 92 : 1 whekas AsPh4C1 switches reaction channels to a 1 : 91 ratio [3]. (c) O/C ratios for the first reaction step G/(H + I) vary between 0.7-1.1 (catalysts: PPhqBr, benzo-15crown-5, NMe4Br) and 21 (catalysts: Kryptofix [2.2.2], (Me2N)3P=N=P(NMe&BF4) [4]. 1).c PI.The present study addresses the question whether catalyst structure influences can also be found in the ZIE diastereoselectivity of Darzens reactions and mechanistically related cyclopropane syntheses from Michael acceptors and a-halocarbanions. In both of these reactions stereoselection occurs before ring closure. We have investigated phase transfer catalytic conversions (i) of benzaldehyde with ethyl chloroacetate to give (Z/E)-2-phenyl-3-ethoxycarbonyloxirane (l), (ii) of benzaldehyde with 2-chloro-2-phenylacetonitrile to yield the isomeric 2-cyano-2,3-diphenyloxiranes (Z), and (iii) of methacrylonitrile with 2-chloropropionitrile to (Z/E)-1,2-dicyano-l,2-dimethylcyclopropane (3) under standardized conditions. Scheme 2Reaction (i) has been the subject of intensive previous studies under non-PTC conditions. Influences of solvent, base and additional substituents were investigated [5,6]. The Makosza group introduced PTC conditions (solid K2CO3, TEBA as catalyst) and observed Z/E ratio of approximately 1 [7]. Further work by a Japanese group showed that this PTC conversion is sensitive towards many factors: concentration of catalyst, molar ratio of reactants, solvent, and temperature [8]. Under certain conditions, the Z/E ratio varied between 0.44 (dibenzo-18-crown-6) and 0.1 (tetrabutylphosphonium bromide).Literature is also available on some previous PTC experiments concerning reaction (ii). Whereas Z/E ratios of almost l was reported for the noncatalyzed process, TEBA and dibenzo-18-crownd gave a value of 8 under certain conditions [9]. Similarly, reaction (iii) has been performed before under PTC by the Polish group of Makosza and Jon'czyk. TEBA gives a Z/E ratio of 0.8 under the conditions used [lo].Our own results are given in Table 1. Because of the mentioned previous experiences, all experiments were conducted under carefully controlled circumstances. The recorded conversions and Z/E ratios are averages of 3-7 runs. Due to the heterogeneous nature of the systems, the...

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Darzens glycidic ester condensation of benzaldehyde in solid-liquid two-phase system

Cited by 7 publications

References 1 publication

Highly Efficient Darzens Reactions Mediated by Phosphazene Bases under Mild Conditions

Highly Efficient Darzens Reactions Mediated by Phosphazene Bases under Mild Conditions

Darzens Condensation

Z/E ratios in Darzens Reactions and Cyclopropanations: Influence of phase transfer catalyst structure

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