Metal Dependent 1,3-Asymmetric Induction in the Retro-[1,4]-Brook Rearrangement of a Silylated Tiglyl Alkalimetal Compound

Gibson, Christoph; Buck, T.; Noltemeyer, Mathias; Brückner, Reinhard

doi:10.1016/s0040-4039(97)00516-9

Cited by 18 publications

(6 citation statements)

References 13 publications

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“…Subsequently, the same group made use of the umpoled species generated from phosphite (±)-9 in catalytic addition reactions to a,b-unsaturated amides. 135 The interesting reaction sequence consists of a [1,2]-Brook rearrangement, a conjugate addition, and a retro- [1,4]-Brook 136 rearrangement. Enantiomerically enriched phosphite (R,R)-9 allowed for a diastereoselective (anti:syn = 10:1), and enantioselective (60% ee for the major diastereomer) transformation (Scheme 50).…”

Section: Nucleophilic Catalysismentioning

confidence: 99%

Air- and Moisture-Stable Secondary Phosphine Oxides as Preligands in Catalysis

Ackermann¹

2006

Synthesis

232

108

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Section: Nucleophilic Catalysismentioning

confidence: 99%

Air- and Moisture-Stable Secondary Phosphine Oxides as Preligands in Catalysis

Ackermann¹

2006

Synthesis

232

108

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“…The proposed catalytic cycle is depicted in Scheme and is initiated by phosphite addition and the [1,2] Brook rearrangement 21. Catalyst release is apparently triggered after conjugate addition by an unusual diastereoselective retro [1,4] Brook rearrangement ( 3 → 10 ) 22. The fact that the major enantiomer possesses the same C3 configuration in both the syn and anti diastereomers (Scheme ) suggests that the chiral phosphite may be the dominant diastereocontrol element rather than a preferred transition‐state topology.…”

Section: Methodsmentioning

confidence: 99%

Metallophosphite‐Induced Nucleophilic Acylation of α,β‐Unsaturated Amides: Facilitated Catalysis by a Diastereoselective Retro [1,4] Brook Rearrangement

et al. 2005

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Nucleophilic acylation of enones and enoates catalyzed by cyanide ions or heterazolium carbenes, commonly known as the Stetter reaction, is a useful method for the synthesis of 1,4-dicarbonyl compounds.[1] The key feature of this reaction is the carbonyl-polarity reversal initiated by the addition of a cyanide ion or a heterazolium carbene to an aldehyde facilitating subsequent 1,4-addition to an a,b-unsaturated carbonyl compound. Although this reaction has proven fruitful with a variety of acceptors, its success has been largely limited to aryl or unsubstituted [2] substrates. Acceptors bearing a b-alkyl group normally give the 1,4-addition product in 30-40 % yield, [3] and achieving enantioselectivity in the intermolecular Stetter reaction has also proven to be difficult.[4] Herein, we provide a strategy to address both of these issues through metallophosphite-catalyzed acylations of a,b-unsaturated amides. These reactions are enabled by an unusual [1,2] Brook rearrangement/conjugate addition/retro [1,4] Brook rearrangement sequence that proceeds with good anti diastereoselectivity and allows access to a range of stable a-silyl-g-ketoamides (Scheme 1).Acyl silanes are effective aldehyde surrogates that confer unique advantages in umpolung reactions. The acyl anion equivalent formed on nucleophilic addition and subsequent [1,2] Brook rearrangement [5,6] undergoes addition to a number of electrophiles. DeglInnocenti et al. found that the 1,4-addition of benzoyl trimethylsilane to cyclohexenone can be catalyzed by cyanide ions, [7] whereas Scheidt and coworkers recently described the successful conjugate addition of acyl silanes to unsaturated esters and ketones by using thiazolium carbene catalysis. [8,9] The substrate scope of the latter process mirrors the classic Stetter reaction, and conjugate acceptors bearing a b-alkyl substituent have not been reported. Metallophosphites [10,11] can be considered as an alternative to cyanide ions and thiazolium carbenes, and they have recently been described as carbonyl-umpolung catalysts in the context of a new enantioselective crossbenzoin reaction.[12] We projected that this catalysis concept might be applicable to alkene electrophiles as well.The conjugate addition of acyl silanes (benzoyl trimethylsilane, benzoyl triethylsilane, and benzoyl dimethylphenylsilane) to Michael acceptors (ethyl crotonate, methyl cinnamate, and cyclohexenone) catalyzed by the Enders phosphite 5 was initially examined. Potassium hydride gave the best reactivity of the bases screened in these reactions; however, few reactions provided appreciable quantities of the desired acylation product. The 1 H NMR spectra of the reactions typically revealed incorporation of the phosphite in the acyl silane/acceptor adduct, thus indicating that the proposed cycle was initiated but not completed. Exposure of the reaction mixture to tetrabutylammonium fluoride (TBAF) afforded the desired g-ketoester. Ethyl crotonate provided the best yields of the acceptors screened, but even under optimized conditions thes...

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“…The allyllithium compound 236 was generated from the phenylsulfanyl precursors by means of lithium naphthalenide in THF at ±78 C in the presence of TMEDA and underwent a irreversible retro-[1,4]-Brook rearrangement to give an almost 4:1 mixture of syn,trans and anti,trans diastereomers [186]. A diastereomeric mixture of isopentenyldimethylcyclopentanols 239 was obtained through a lithium-ene cyclization starting from the oxido allylic intermediate 238, which was generated by LiDTBB carbon±sulfur bond cleavage of 237, the lithium oxide unit facilitating the cyclization.…”

Section: Remote Allyl and Benzyllithium Compoundsmentioning

confidence: 99%

Polyfunctional Lithium Organometallics for Organic Synthesis

Yus¹,

Foubelo²

2005

Handbook of Functionalized Organometallics

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Multifunctional organic molecules can be achieved by reacting functionalized organolithium compounds [1] with electrophilic reagents, this fact makes these intermediates of relevant interest in synthetic organic chemistry [2]. Another remarkable fact concerning organolithium compounds, compared with other organometallic compounds is that they can be prepared following a great number of different methodologies [3]: hydrogen±lithium exchange (deprotonation), halogen±lithium exchange, transmetallation reactions, carbon±heteroatom bond cleavage and carbolithiation of multiple carbon±carbon bonds. However, the highly ionic character of the carbon±lithium bond [4] makes these compounds extremely reactive and also unstable, so the synthetic processes should be carried out in some cases under very mild reaction conditions.Regarding the stability of functionalized organolithium compounds, it depends mainly on three factors, the most important one being the compatibility of the functional group with the carbon±lithium bond, so in some cases the functionality should be protected. The hybridization of the carbon atom bonded to the lithium atom is also important, so sp derivatives are more stable than the corresponding sp 2 and these are more stable than the sp 3 ones as it happens to the corresponding carbanions. Finally, the relative position of the functionality and the carbanionic center is also relevant, probably the b-functionalized derivatives being the most unstable species due to the existence of two consecutive carbon atoms with opposite polarities, the b-elimination process to give an olefin is extremely favored. Stabilized organolithium compounds, such as lithium enolate intermediates [5], a-organolithium compounds bearing electron-withdrawing groups (RSO, RSO 2 , CN, NO 2 , etc.) and heteroatoms such as sulfur [6], selenium and phosphorus as well as functionalized aryllithium compounds will not be consider in depth in this chapter due to the limited length of this review.The following study is ordered based on the relative position of the functionality and the carbanionic center, as well as on the hybridization of that center.

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Metal Dependent 1,3-Asymmetric Induction in the Retro-[1,4]-Brook Rearrangement of a Silylated Tiglyl Alkalimetal Compound

Cited by 18 publications

References 13 publications

Air- and Moisture-Stable Secondary Phosphine Oxides as Preligands in Catalysis

Air- and Moisture-Stable Secondary Phosphine Oxides as Preligands in Catalysis

Metallophosphite‐Induced Nucleophilic Acylation of α,β‐Unsaturated Amides: Facilitated Catalysis by a Diastereoselective Retro [1,4] Brook Rearrangement

Polyfunctional Lithium Organometallics for Organic Synthesis

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