Cross Silyl Benzoin Additions Catalyzed by Lanthanum Tricyanide

Bausch, Cory C.; Johnson, Jeffrey S.

doi:10.1021/jo0496143

Cited by 32 publications

(11 citation statements)

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“…Our laboratory has developed the use of acyl silanes as acyl anion equivalents in the racemic and enantioselective cross silyl benzoin reaction. Additionally, we have found La(CN) 3 to be a particularly reactive catalyst for promoting the cross silyl benzoin between acyl silanes and aldehydes, with reaction times under 5 min . We postulated that under La(CN) 3 catalysis we might be able to engage ketone electrophiles with acyl silanes.…”

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confidence: 94%

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Lanthanum Tricyanide-Catalyzed Acyl Silane−Ketone Benzoin Additions

Tarr

Johnson

2009

Org. Lett.

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Lanthanum tricyanide efficiently catalyzes a benzoin-type coupling between acyl silanes and ketones. Yields range from moderate to excellent over a broad substrate scope encompassing aryl, alkyl, electron-rich, and sterically hindered ketones.α-Hydroxycarbonyls are valuable building blocks for numerous targets in organic synthesis. 1 The benzoin addition provides direct access to α-hydroxy ketones and its strategic application has grown in the past decade. In addition to traditional metal cyanide catalysts, 2 N-heterocyclic carbenes and metallophosphites have been identified as efficient asymmetric catalysts for intramolecular and intermolecular benzoin reactions 3 and the cross silyl benzoin reaction. 4 Despite the wide range of electrophiles that have been successfully engaged by acyl anion equivalents in the benzoin and cross silyl benzoin reactions, the direct catalytic coupling of acyl anion equivalents to ketones remains a challenge due to the lower reactivity of ketones that presumably permits nonproductive enolization to become competitive. Stoichiometric methods for ketone acylation do exist; however, general strategies are not in place for conducting those reactions asymmetrically. 5 Suzuki, 6, 3c Enders, 7, 3d and You 8 have reported carbene-catalyzed intramolecular aldehyde-ketone benzoin cyclization for the formation of five-and six-membered rings. Asymmetric variants for the intramolecular reaction have also been reported that proceed in up to 98% yield and 99% ee. 6b, 7, 8 The single example of intermolecular catalytic ketone acylation comes from the recent work of Demir and coworkers, 9 who described the cyanide-catalyzed coupling of acyl phosphonates 10 with ketones in chemical yields of 41-95%; however, the reaction is largely limited to electron-poor ketones. In general, enolizable protons were replaced with fluorine while ortho-substituted aryl and aryl-methyl ketones typically failed to give the desired product. Tuning of the reaction conditions and/or addition of a co-catalyst (Cu(OTf) 2 or thiourea) was required for certain substrate combinations. Our laboratory has developed the use of acyl silanes as acyl anion equivalents in the racemic 11 and enantioselective 4 cross silyl benzoin reaction. Additionally, we have found La (CN) 3 to be a particularly reactive catalyst for promoting the cross silyl benzoin between acyl silanes and aldehydes, with reaction times under 5 minutes. 12 We postulated that under La (CN) 3 catalysis, we might be able to engage ketone electrophiles with acyl silanes. We were hopeful that these conditions might lead to a more general reaction for intermolecular ketone acylation. Pitfalls to be navigated in this variant include undesired dimerization of the acyl silane, nonproductive proton transfer between the (silyloxy)nitrile anion intermediate and the ketone electrophile, and potential retro-benzoin reaction 13 of the α-siloxy ketone product (Figure 2).Gratifyingly, acyl silane 1a reacted with one equivalent of acetophenone in the presence of 20 mo...

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confidence: 94%

“…Additionally, we have found La(CN) 3 to be a particularly reactive catalyst for promoting the cross silyl benzoin between acyl silanes and aldehydes, with reaction times under 5 minutes 12. We postulated that under La(CN) 3 catalysis, we might be able to engage ketone electrophiles with acyl silanes.…”

mentioning

confidence: 95%

Lanthanum Tricyanide-Catalyzed Acyl Silane−Ketone Benzoin Additions

Tarr

Johnson

2009

Org. Lett.

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“…O procedimento clássico desta etapa envolve uma reação promovida em meio alcalino com a presença de íons cianeto, formando um carbânion estável com um grupamento nitrila. 16 Assim, devido à toxicidade da reação e de seus reagentes, essa reação é sempre realizada sob capela de exaustão, e o resíduo gerado é tratado com sulfato de ferro (II), com o intuito de gerar um complexo menos tóxico e passível de tratamento posterior, o hexacianoferrato (II) de ferro (III). 17 Na busca de catalisadores menos tóxicos, como alternativas já descritas na literatura para os íons cianeto, estão a tiamina, 18 bem como sais de tiazol em meio alcalino, 19 carbenos heteroazólios 20 e metalofosfitos.…”

Section: Resultsunclassified

Síntese da fenitoína assistida por micro-ondas: proposta de aula prática para alunos de graduação

Konrath¹,

Piedade²,

Eifler‐Lima³

2012

Quím. Nova

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“…On the other hand, Johnson later demonstrated that the counter ion (M + ) in MCN catalysis is highly critical, and that one lanthanum tricyanide (La(CN) 3 ) was identified as the optimal catalysts after screening of various metal cyanides. 52 Acyl silanes are not only useful acyl anion precursors but also good catalysts to achieve regioselective benzoin-type products in one step. Nowadays, cyanide-catalyzed silyl benzoin reactions play a prominent and practical role in cross-benzoin condensation reactions.…”

Section: Cyanide Ion Catalyzed Umpolung Reactionsmentioning

confidence: 99%

Umpolung strategy: Advances in catalytic C-C bond formations

Eymür

Göllü²,

Tanyeli

2013

Turk J Chem

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This mini-review examines the recent advances in umpolung strategy, devised originally by Corey and Seebach. Although numerous stoichiometric variants have been published to date, this article covers just the catalytic C-C bond forming reactions due to their major benefits such as atom economy, less pollution, and workable simplicity.In the context of umpolung, the studies are evaluated under 3 main titles: enzyme, N -heterocyclic carbene, and cyanide ion catalyzed reactions. In particular, enzyme and NHC catalyzed reactions mainly involve asymmetric applications.

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Cross Silyl Benzoin Additions Catalyzed by Lanthanum Tricyanide

Cited by 32 publications

References 20 publications

Lanthanum Tricyanide-Catalyzed Acyl Silane−Ketone Benzoin Additions

Lanthanum Tricyanide-Catalyzed Acyl Silane−Ketone Benzoin Additions

Síntese da fenitoína assistida por micro-ondas: proposta de aula prática para alunos de graduação

Umpolung strategy: Advances in catalytic C-C bond formations

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