Solid-liquid phase transfer catalysis without solvent

Loupy, André; Sansoulet, J.; Zaparucha, Anne; Mérienne, C.

doi:10.1016/s0040-4039(00)95194-3

Cited by 61 publications

(14 citation statements)

References 14 publications

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“…In the thermodynamic enolate, the phenyl group and the enolate are planar and the interaction with the ephedrinium salt is more effective (figure 3). In solvent-free conditions the effect must be enhanced (9). As a preliminary conclusion, ephedrinium salts produce an effect not previously described, a change in regioselectivity.…”

Section: Regioselectivitymentioning

confidence: 57%

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Michael Addition of 2-Phenylcyclohexanone to Chalcone Under Phase-Transfer Catalysis Conditions

Dı́ez-Barra¹,

Hoz²,

Merino³

et al. 1997

ACS Symposium Series

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The regioselectivity in the Michael addition of 2-phenylcyclohexanone to chalcone can be controlled by the appropriate choice of PTC conditions. In the absence of solvent, and using ephedrinium salts as catalyst, 2-substituted derivatives are predominant, while solid-liquid conditions and TBAB afford mainly 6-substituted derivatives. A stabilizing π-π interaction between the ephedrinium salt and the thermodynamic enolate is proposed to explain the results. A transition state with the participation of the metal ion is suggested to explain the obtained diastereoselectivity.Michael addition is one of the most useful reactions in organic synthesis (1,2). The required basic catalysis for this reaction can efficiently be carried out by PTC methods. In the last twenty years, addition of acetamidomalonate (3,4), 2,4-pentanodione (5), methyl acetoacetate (5), fluorene (5), substituted indanones (6), nitroalkanes (7), thiolate (7), cyanide (8), and methyl phenylacetate (8) anions to a large number of Michael acceptors, mainly α,β-unsaturated ketones, under PTC have been reported.Several approaches to the stereochemical control in the Michael addition and the alkylation of enolates have been envisaged. One of these is the use of chiral phase transfer catalysts. In this field, chiral crown ethers (8), quininium (7), ephedrinium (9-11), cinchoninium and cinchonidinium (13-20) salts have been used.In most cases a π-π interaction between the catalyst and one of the reactants has been proposed to justify the enantiomeric and diastereomeric excesses achieved. Two types of interactions have been suggested: i) enolate-catalyst ( figure 1, a and b) ii) substrate-catalyst ( figure 1, c).In the first case the catalyst blocks preferentially one face of the enolate, while the second case represents a higher accessibility of one face of the Michael acceptor.The enolate-catalyst interaction has been studied in the alkylation of benzophenone Schiff bases (14-17) and 2-substituted indanones

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Section: Regioselectivitymentioning

confidence: 57%

“…One of these is the use of chiral phase transfer catalysts. In this field, chiral crown ethers (8), quininium (7), ephedrinium (9)(10)(11), cinchoninium and cinchonidinium (13)(14)(15)(16)(17)(18)(19)(20) salts have been used.…”

mentioning

confidence: 99%

Michael Addition of 2-Phenylcyclohexanone to Chalcone Under Phase-Transfer Catalysis Conditions

Dı́ez-Barra¹,

Hoz²,

Merino³

et al. 1997

ACS Symposium Series

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“…Sais derivados de efedrina 69 foram efetivos na adição assimétrica de N-acetamidomalonato de dietila à chalcona (Esquema 7), sendo que as reações realizadas em ausência de solvente levaram a produtos com maiores valores de e.e. (próximos a 60%).…”

Section: Esquema 6 Figura 18 Proposta De Par Iônico Formado Entre O unclassified

“…A associação deste complexo doador-catalisador com a chalcona estabelecer-se-ia através de uma ligação de hidrogênio entre o grupo NH, do enolato do N-acetamidomalonato, e a carbonila do aceptor. Neste sentido, a reação estudada por Loupy e col. 69,70 é um caso bastante particular em que a estrutura do doador tem papel fundamental e favorável à indução de assimetria.…”

Section: Quadro 1 Algumas Reações Em Ctf Catalisadas Por Sais De Alaunclassified

Catálise de transferência de fase

Lucchese¹,

Marzorati²

2000

Quím. Nova

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Recebido em 27/4/99; aceito em 30/3/00 PHASE TRANSFER CATALYSIS -Since its discovery, phase transfer catalysis (PTC) has grown considerably and nowadays is one of the most versatile preparative methods. The search for new catalysts, their use in PTC asymmetric synthesis and the attempts to understand their mechanistic role are modern and exciting topics of investigation. A review on main achievements in the last two decades is presented.Keywords: phase transfer catalysis; quaternary ammonium salts; asymmetric synthesis. REVISÃO INTRODUÇÃOA catálise de transferência de fase (CTF) é um método utilizado para provocar ou acelerar a reação entre substâncias que estão dissolvidas em ou que constituem fases diferentes, pela atuação de um agente transferidor. Este agente ou catalisador forma um par iônico com a espécie química da fase aquosa ou sólida, que dessa forma é extraída para a fase orgânica, reagindo com o substrato ali presente.Do ponto de vista preparativo apresenta várias vantagens sobre os métodos clássicos, tais como 1 : ♦ utilização de solventes sem a necessidade de tratamentos prévios para torná-los anidros. ♦ aumento da velocidade de reação e/ou emprego de temperaturas menores. ♦ uso de hidróxidos e carbonatos alcalinos em lugar de reagentes como hidretos, amidetos e alcóxidos. ♦ simplicidade operacional.A CTF foi utilizada como técnica preparativa a partir da metade dos anos 60 por grupos independentes de pesquisadores, Bränsdtröm na Suécia 2,3 , Makosza na Polônia 4-8 e Starks 9-11 nos EUA, apesar de alguns relatos anteriores 12 serem conhecidos. Desde seu surgimento, houve um grande avanço na compreensão de seus aspectos mecanísticos e na aplicação dessa técnica a um grande espectro de reações, muitas das quais utilizadas para a síntese de fármacos, perfumes, polímeros e outros produtos de interesse industrial 13 . A primeira proposta mecanística para o processo de transferência de fase foi formulada por Starks 10 , para a CTF líquido-líquido (CTF-LL), com distribuição do catalisador entre as fases aquosa e orgânica. A extração de um reagente Y -para a fase orgânica e a reação subsequente ocorrem devido à formação de um par iônico deste com o sal de ônio. um requisito básico para a catálise, principalmente no caso de catalisadores muito lipofílicos, e que a formação do par iônico entre o sal de ônio e o ânion do reagente poderia ocorrer na interface do sistema. De uma maneira geral, estes mecanismos formulados para CTF-LL, em meio neutro, podem ser aplicados para reações em presença de bases como hidróxidos de metais alcalinos. Reações de ácidos com pKa inferior a 22 poderiam ocorrer através de mecanismos análogos aos propostos para meio neutro. Ácidos relativamente fortes como acetilacetona dissolvem-se em soluções aquosas de NaOH e o carbânion ou enolato formados podem ser extraídos pelo cátion Q + para a fase orgânica 1 . Entretanto, para ácidos orgânicos mais fracos com pKa entre 22 e 25, como a fenilacetonitrila, Makosza sugeriu um mecanismo interfacial 15 . Neste caso, a desprotonação da molécu...

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“…Our recent development of cupreinium salts 1, as highly enantioselective phase-transfer catalysts for an asymmetric Darzens reaction, [12] prompted us to explore them for the asymmetric conjugate addition of cyanide. Similar to other known bifunctional phase-transfer catalysts that bear a hydrogen-bond-donor moiety, [13][14][15] cupreidinium salts CPD-1, could in principle mediate phasetransfer catalysis by their association with an anionic cyanation species, presumably a cyanide or cyanoalkoxide ion, by simultaneous ion-pair and hydrogen-bonding interactions (I, Scheme 1). Alternatively, CPD-1 could promote the conjugate addition by simultaneous interactions with both the cyanation species and the enone (II, Scheme 1).…”

mentioning

confidence: 94%

Structural Study‐Guided Development of Versatile Phase‐Transfer Catalysts for Asymmetric Conjugate Additions of Cyanide

et al. 2011

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Significant advances have been made in the development of catalytic 1,2-asymmetric cyanations using both chiral metal and organic catalysts. [1] In contrast, only a few highly enantioselective catalytic conjugate additions of cyanide ions have been realized despite the potential of such transformations in providing efficient enantioselective access to synthetically valuable chiral building blocks. [2] The first breakthroughs were reported by Jacobsen and co-workers, who described chiral Al-Salen [3] and bimetallic cooperative catalyst systems [4] for the enantioselective conjugate additions of trimethylsilyl cyanide (TMSCN) to a,bunsaturated imides. Shibasaki, Kanai, and co-workers reported two chiral bifunctional catalysts derived from gadolinium, strontium, and different asymmetrically prepared or carbohydrate-based chiral ligands for a highly enantioselective 1,4-addition of cyanide with HCN/trialkylsilyl cyanides to a,b-unsaturated N-acyl pyrroles [5] and enones, [6] respectively. Feng [7] and co-workers have reported a modular titanium catalyst for the cyanation of alkylidine malonates. Very recently, Ohkuma [8] and co-workers disclosed a chiral Ru complex for the conjugate addition of TMSCN to enones. These existing reactions, while representing remarkable success in establishing general substrate scope and high catalyst efficiency, require the use of various trialkylmetal cyanides in super-stoichiometric amounts. Thus, we became interested in the development of highly enantioselective catalytic 1,4-additions of cyanide with readily accessible and easy to handle cyanation reagents.Chiral phase-transfer catalysis has been developed as an effective strategy for the activation of practical cyanation reagents, such as KCN [9] and acetone cyanohydrin, [10] for asymmetric 1,2-additions of cyanides. On the other hand, this strategy has so far been attempted only with 1,4-additions of cyanide to nitroalkenes. [11] These attempts have so far been met with limited success. Our recent development of cupreinium salts 1, as highly enantioselective phase-transfer catalysts for an asymmetric Darzens reaction, [12] prompted us to explore them for the asymmetric conjugate addition of cyanide. Similar to other known bifunctional phase-transfer catalysts that bear a hydrogen-bond-donor moiety, [13][14][15] cupreidinium salts CPD-1, could in principle mediate phasetransfer catalysis by their association with an anionic cyanation species, presumably a cyanide or cyanoalkoxide ion, by simultaneous ion-pair and hydrogen-bonding interactions (I, Scheme 1). Alternatively, CPD-1 could promote the conjugate addition by simultaneous interactions with both the cyanation species and the enone (II, Scheme 1).We first investigated the asymmetric conjugate addition of acetone cyanohydrin to enone 5 a. As the equilibrium between cyanohydrin and the enone is known to favor the latter under basic conditions, [16] we reasoned that chiral phase-transfer catalysis might provide an attractive strategy to address the 1,2-vs. 1,4-chemoselectivity ...

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Solid-liquid phase transfer catalysis without solvent

Cited by 61 publications

References 14 publications

Michael Addition of 2-Phenylcyclohexanone to Chalcone Under Phase-Transfer Catalysis Conditions

Michael Addition of 2-Phenylcyclohexanone to Chalcone Under Phase-Transfer Catalysis Conditions

Catálise de transferência de fase

Structural Study‐Guided Development of Versatile Phase‐Transfer Catalysts for Asymmetric Conjugate Additions of Cyanide

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