N-trialkylsilyldiphenylcetenimines: Action sur des derives carbonyles

Cazeau, P.; Llonch, J. P.; Simonin-Dabescat, F.; Frainnet, E.

doi:10.1016/s0022-328x(00)88950-0

Cited by 13 publications

(15 citation statements)

References 4 publications

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“…13 Despite this promising result, no subsequent reports have appeared on the enantioselective 1,4-additions of SKIs to conjugated carbonyl compounds. Herein we report our initial studies on the Lewis base catalyzed, SiCl 4 -mediated additions of disubstituted silyl ketene imines to a,b-unsaturated aldehydes and ketones for the catalytic, diastereoselective, and enantioselective construction of quaternary stereogenic centers.…”

Section: Methodsmentioning

confidence: 99%

Construction of Quaternary Stereogenic Carbon Centers by the Lewis Base Catalyzed Conjugate Addition of Silyl Ketene Imines to α,β-Unsaturated Aldehydes and Ketones

Denmark¹,

Wilson²

2010

Synlett

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C o n s t r u c t i o n o f Q u a t e r n a r y S t e r e o g e n i c C a r b o n C e n t e r s Abstract: Highly site-selective Mukaiyama-Michael additions of silyl ketene imines to a,b-unsaturated aldehydes and ketones are described. The combination of silicon tetrachloride and a chiral bisphosphoramide provides an effective catalyst system for promoting the addition of silyl ketene imines to a variety of aromatic enals with high site selectivity and moderate to good diastereo-and enantioselectivity.The catalytic, enantioselective synthesis of compounds containing quaternary stereogenic carbon centers continues to provide organic chemists with challenges for catalyst design and reaction development. 1 The key issue in the construction of these centers is to identify catalyst systems that can overcome the substantial steric encumbrance encountered in the carbon-carbon bond-forming event, while still providing an effective environment for obtaining high asymmetric induction. Although a number of elegant solutions have recently been devised for achieving this goal, certain types of reaction frameworks still present significant obstacles and provide platforms for novel catalyst design and innovation in synthetic methods.An important transformation that presents promising opportunities for setting quaternary stereogenic centers is the Michael reaction. 2 This venerable process has long been recognized as one the most reliable methods for carbon-carbon bond formation as it allows for the preparation of the synthetically useful class of 1,5-dicarbonyl compounds. Moreover, the high exothermicity of the catalytic Michael reaction provides the energy needed to overcome the steric strain of setting a quaternary center. The successful implementation of a catalytic, enantioselective variant of this reaction 3 requires a catalyst that can control the relative and absolute topicity for the combination of two fully substituted sp 2 centers. For activation of the nucleophile, the catalyst has to control the configuration of a disubstituted enolate. On the other hand, activation of the electrophile requires the catalyst to be coordinated selectively at one of the binding sites of the Lewis basic oxygen (anti vs. syn, Scheme 1) and also control the conformation of the conjugated double bonds in the acceptor (s-cis vs. s-trans, Scheme 1). 4 In recent years, creative solutions to these challenges have appeared that provide Michael addition products containing quaternary stereogenic carbons in good yield and high selectivity. 1,2 Scheme 1Despite these achievements some limitations still exist for certain combinations of donors and acceptors. For example, existing methods are limited to readily enolizable carbonyl compounds, such as b-keto esters, a-cyano ketones, and b-diketones in combination with acyclic and cyclic ketones. The addition of simple ketones, esters or nitriles to a,b-unsaturated aldehydes or ketones finds no general solution for the synthesis of quaternary stereogenic carbon centers because of the problem of controlli...

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Section: Methodsmentioning

confidence: 99%

Construction of Quaternary Stereogenic Carbon Centers by the Lewis Base Catalyzed Conjugate Addition of Silyl Ketene Imines to α,β-Unsaturated Aldehydes and Ketones

Denmark¹,

Wilson²

2010

Synlett

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“…Two important advantages result from this approach: some of the issues associated with α‐anion nitriles6 will be avoided, and the reaction of SKIs with aldehydes will generate highly versatile α‐hydroxy nitriles, which may then be converted into more complex molecules 5c,7. The reaction of SKIs with benzaldehyde, crotonaldehyde, and ketones has been reported by Frainnet et al8 More recently, Denmark's group reported, in a series of papers, the enantioselective construction of two chiral centres derived from the sp 2 carbon in the starting aldehyde and tertiary carbon in the nitrile, by the Lewis‐base‐catalysed addition of SKIs to aldehydes 5c,9…”

Section: Introductionmentioning

confidence: 91%

Efficient Aldol‐Type Reaction of O‐Protected α‐Hydroxy Aldehydes and N‐Trimethylsilyl Ketene Imines: Synthesis of β,γ‐Dihydroxy‐Nitriles

et al. 2013

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An uncatalyzed aldol‐type reaction of aromatic N‐trimethylsilyl ketene imines with O‐protected α‐trialkylsilyloxy or α‐benzyloxy aldehydes is reported. It is shown that N‐trimethylsilyl ketene imines (SKIs) are essential for the success of this aldol‐type reaction, and that almost complete control of stereochemistry in the formation of the stereocentre vicinal to the stereogenic centre present in the starting aldehyde is seen when these compounds are used. A very high syn stereoselectivity was observed at room temperature, and a reversal of stereoselectivity to favour the formation of the anti product may be achieved at low temperature. Preliminary theoretical calculations support the hypothesis that the aldol‐type reaction is facilitated by the formation of a cyclic transition state, with concomitant silatropic migration from the ketene imine‐nitrogen to the aldehyde oxygen. The catalyst‐free aldol reaction has been applied to aromatic N‐trimethylsilyl ketene imines bearing two different aromatic groups. In these reactions, the diastereoselectivity for the stereocentre arising from aldehyde sp2 carbon remained extremely high, but the stereoselectivity for the formation of the new quaternary stereocentre was unsatisfactory.

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“…[20] Bei der Addition von 10 an Zimtaldehyd wurden 1,4-und 1,2-Additionsprodukte im Verhältnis 63:37 ( Die C-Acylierung von 10 mit Acylchloriden wurde von Frainnet und Mitarbeitern ebenfalls untersucht. [21] Die Reaktionen wurden ohne Promotor und Lçsungsmittel durchgeführt und ergaben in hohen Ausbeuten die b-Ketonitrilprodukte 19 (Schema 11).…”

Section: Aldol-und Michael-reaktionunclassified

“…Eine frühe Verçffentlichung von Frainnet und Mitarbeitern beschreibt Carbonyladditionen von SKIs. [20] Die Autoren wiesen nach, dass es sich bei SKIs um Kohlenstoffnucleophile handelt, die zur Addition an eine Reihe von Carbonylelektrophilen fähig sind, einschließlich aromatischen Aldehyden, a,b-ungesättigten Aldehyden, Ketonen und Carbonsäurehalogeniden. Beispielsweise führte die lçsungsmittelfreie Kombination von N-(Trimethylsilyl)diphenylketenimin (10) mit Benzaldehyd zu einer exothermen Reaktion, aus der in hoher Ausbeute das entsprechende b-Silyloxynitril 16 isoliert werden konnte (Schema 8).…”

Section: Aldol-und Michael-reaktionunclassified

“…Beispielsweise führte die lçsungsmittelfreie Kombination von N-(Trimethylsilyl)diphenylketenimin (10) mit Benzaldehyd zu einer exothermen Reaktion, aus der in hoher Ausbeute das entsprechende b-Silyloxynitril 16 isoliert werden konnte (Schema 8). [20] Ein elektronenarmer aromatischer Aldehyd, 4-Chlorbenzaldehyd, geht ebenfalls in hoher Ausbeute eine Addition ein. Es gab allerdings keine weiteren Untersuchungen zur Anwendungsbreite dieser Reaktion in Bezug auf das Nucleophil oder andere Aldehyde.…”

Section: Aldol-und Michael-reaktionunclassified

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Silylketenimine – vielseitige Nucleophile für die katalytische asymmetrische Synthese

Denmark

Wilson

2012

Angewandte Chemie

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Dieser Kurzaufsatz bietet einen Überblick über die Entwicklung von Silylketeniminen und deren jüngste Anwendungen in katalytischen enantioselektiven Reaktionen. Die einzigartige Struktur von Keteniminen macht verschiedenste Reaktionsmuster möglich und liefert Lösungen für die bestehenden Herausforderungen beim enantioselektiven Aufbau von quartären Kohlenstoffstereozentren und Kreuz‐Benzoinaddukten. Es wird eine Vielzahl an Reaktionen präsentiert, bei denen Silylketenimine eingesetzt wurden. Unser Ziel ist dabei, zum Nachdenken über neue Anwendungsmöglichkeiten dieser nur unzureichend genutzten Nucleophile anzuregen.

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N-trialkylsilyldiphenylcetenimines: Action sur des derives carbonyles

Cited by 13 publications

References 4 publications

Construction of Quaternary Stereogenic Carbon Centers by the Lewis Base Catalyzed Conjugate Addition of Silyl Ketene Imines to α,β-Unsaturated Aldehydes and Ketones

Construction of Quaternary Stereogenic Carbon Centers by the Lewis Base Catalyzed Conjugate Addition of Silyl Ketene Imines to α,β-Unsaturated Aldehydes and Ketones

Efficient Aldol‐Type Reaction of O‐Protected α‐Hydroxy Aldehydes and N‐Trimethylsilyl Ketene Imines: Synthesis of β,γ‐Dihydroxy‐Nitriles

Silylketenimine – vielseitige Nucleophile für die katalytische asymmetrische Synthese

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