High coordinate germanium and tin complexes in the allylation reactions of aldehydes

Hada, Masahiko; Nakatsuji, Hideaki; Ushio, J.; Izawa, Mondo; Yokono, Hitoshi

doi:10.1021/om00033a008

Cited by 10 publications

(11 citation statements)

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“…Pentacoordinated silicon species have been studied extensively both from experimental and from theoretical viewpoints. − In many cases, those species are assumed to intervene as stable intermediates in reactions. ,, High reactivities of silicon compounds and high stereoselectivities in reactions have been interpreted successfully by invoking pentacoordinated intermediates. One of those examples involving a pentacoordinated silicon species is the reaction between allylsilanes and carbonyl compounds. − Kira suggested the following mechanism (Scheme ) 1 …”

Section: Introductionmentioning

confidence: 99%

“…One of those examples involving a pentacoordinated silicon species is the reaction between allylsilanes and carbonyl compounds. [27][28][29][30][31][32] Kira suggested the following mechanism (Scheme 1). 31 On the other hand, Oshima and collaborators revealed that there was a marked difference between allylphenylsilacyclobutane and allylphenyldimethylsilane in their reactivities against benzaldehyde.…”

Section: Introductionmentioning

confidence: 99%

“…[27][28][29][30][31][32] Kira suggested the following mechanism (Scheme 1). 31 On the other hand, Oshima and collaborators revealed that there was a marked difference between allylphenylsilacyclobutane and allylphenyldimethylsilane in their reactivities against benzaldehyde. 33 While heating of a mixture of the former and benzaldehyde at 130 °C for 12 h under argon provided 1-phenyl-3-buten-1-ol in 85% yield, the latter resulted in the recovery of starting materials after heating with benzaldehyde at 160 °C for 24 h (Scheme 2).…”

Section: Introductionmentioning

confidence: 99%

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Theoretical Study of the Reaction of Allylsilanes with Carbonyl Compounds

1996

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We have studied the reaction of allylsilanes with aldehydes by applying the ab initio MO theory. It has been shown that the reaction takes place via a transition state involving pentacoordinated silicon species. The oxygen of aldehyde attacks an apical site of the silicon center, while the allyl group departs directly from an equatorial site without causing a pseudorotation. The calculation has shown that the reaction of an allylsilacyclobutane model with formaldehyde has a lower activation barrier than the reaction of allylsilane or methyl-substituted allylsilanes. The barrier height is shown to be correlated well with the angle of coordination of substituents on the silicon center. The reactivity of allylsilanes against nucleophiles is discussed by evaluating the local acidic strength of the reaction site.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Theoretical Study of the Reaction of Allylsilanes with Carbonyl Compounds

1996

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“…Most of the theoretical studies carried out so far on the allylation reactions using allylsilane support the mechanism in which a chairlike six-membered cyclic transition state intervenes in the course of the reaction, ,,, except for the Lewis acid promoted cases. , Kočovský and co-workers recently performed kinetic and DFT studies of the allylation of aldehydes with trichlorosilane catalyzed by QUINOX and showed that the reaction is likely to proceed via a hexacoordinated transition state involving a QUINOX molecule . The allylation reaction promoted by a fluoride ion has also been investigated theoretically. ,, The basicity of the neutral Lewis bases should be much lower compared with that of anionic Lewis bases, such as a fluoride ion. It appears, therefore, to be worthwhile to examine how the allylation of aldehydes and ketones by allyltrichlorosilanes is promoted in the presence of those neutral Lewis bases.…”

Section: Introductionmentioning

confidence: 96%

“…Allylation of aldehydes and ketones with allylsilanes is one of the most useful tools in organic synthesis. − Hosomi et al found that a variety of aldehydes and ketones are allylated with allyltrimethylsilane in the presence of a stoichiometric amount of Lewis acids to afford the corresponding homoallyl alcohols. The reaction provides a very popular strategy for the formation of C−C bonds. − Kira et al reported, on the other hand, that highly stereoselective allylations of aldehydes are achieved by introducing strongly electronegative fluoride and/or alkoxy ligands to allylsilanes. − Theoretical calculations suggested that the reaction should start from pentacoordinate allylsilicates and proceed via a chairlike six-membered cyclic transition state. , This is in contrast with the Lewis acid promoted allylation reactions reported by Hosomi et al, for which an acyclic transition state between a Lewis acid catalyzed aldehyde or ketone species and an allylsilane molecule has been proposed. , …”

Section: Introductionmentioning

confidence: 99%

Quantum-Chemical Study of Neutral Lewis Base Catalyzed Allylation of Aldehydes with Allyltrichlorosilanes

Sakata

Fujimoto

2010

Organometallics

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Calculations at the MP2/6-31G** level of theory show that the activation barrier of the allylation reaction between benzaldehyde and allyltrichlorosilane with the aid of a neutral Lewis base, N,Ndimethylformamide (DMF) or hexamethylphosphoric triamide (HMPA), is considerably lower than that of the reaction in the absence of the Lewis base. An orbital analysis indicates that the electrondonating ability of the γ-carbon in the allyl group is enhanced by the coordination of a DMF or HMPA molecule. The silicon having a hexacoordinated bond arrangement shows an electronaccepting ability or Lewis acidity significantly stronger than that in silicon having a pentacoordinated structure to facilitate the coordination of DMF or other neutral Lewis bases. On the other hand, the electron-accepting level of the orbital that is left for the bond formation with the attacking aldehyde is elevated by the preceding coordination of a neutral base. The orbital is seen, however, to be localized more efficiently on the silicon center in the hexacoordinated transition state. The two Si-Cl bonds that are approximately perpendicular to the Si-O bond being formed and the Si-C bond being broken are strongly polarized at the transition state, reducing the repulsive interaction with the attacking aldehyde. These make up for the weakened electron-accepting ability of the silicon and, therefore, the combined coordination of the aldehyde and a neutral base recovers most of the destabilization associated with the changes in reagent and reactant structures to give the hexacoordinated transition state.

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