Stereoselectivite et regioselectivite de l'alkylation d'epoxydes par les “ates” complexes : Tetrabutylaluminate de lithium et tetraethylaluminate de sodium.

Boireau, G.; Abenhaïm, D.; Bernardon, C.; Henry-Basch, Erica; Sabourault, B.

doi:10.1016/s0040-4039(00)75167-7

Cited by 21 publications

(5 citation statements)

References 6 publications

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“…Complexation leads to a decreased electron density on the epoxide ring, facilitating the nucleophilic attack. While Me 3 Al does work better as a promoter than BF 3 it may not be ideal because Me 3 Al can also attack the epoxide ring. , This could explain why the grafting yield decreased slightly when the AlMe 3 :living end ratio was increased from 0.1 to 0.2.…”

Section: Resultsmentioning

confidence: 99%

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Synthesis of Arborescent Isoprene Homopolymers

Yuan

Gauthier

2005

Macromolecules

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A method was developed for the preparation of isoprene homopolymers with a dendritic architecture using an anionic "grafting onto" methodology. A linear polyisoprene substrate with a high (95%) 1,4-content was first epoxidized to introduce grafting sites randomly along the chain. Coupling of the epoxidized polyisoprene with polyisoprenyllithium yielded a comb-branched or generation G0 arborescent polyisoprene. N,N,N′,N′-Tetramethylethylenediamine, BF 3, Me3Al, LiCl, and LiBr were investigated as promoters for the coupling reaction. Lithium salts were most effective, increasing the grafting yield from 78% to 92% for a linear substrate. Further epoxidation and grafting of the G0 polyisoprene led to arborescent isoprene homopolymers of generations G1 and G2. The attempted synthesis of a G3 arborescent polyisoprene was unsuccessful. The graft polymers were purified by precipitation fractionation and characterized by size exclusion chromatography (SEC), light scattering, and NMR spectroscopy. The products have narrow molecular weight distributions (M w/Mn e 1.05) consistent with a uniform molecular size and display geometric increases in molecular weight and branching functionality for successive generations. The absolute weight-average molecular weight values determined from light scattering measurement are much higher than the apparent SEC values because of the highly branched structure of the molecules.

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Section: Resultsmentioning

confidence: 99%

“…While Me 3 Al does work better as a promoter than BF 3 it may not be ideal because Me 3 Al can also attack the epoxide ring. 35,36 This could explain why the grafting yield decreased slightly when the AlMe 3 :living end ratio was increased from 0.1 to 0.2. Lithium Salt Promoters.…”

Section: Resultsmentioning

confidence: 99%

Synthesis of Arborescent Isoprene Homopolymers

Yuan

Gauthier

2005

Macromolecules

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“…The use of Et 2 O or THF, solvents able to coordinate Li or Na, results in low or no conversion, suggesting a possible activating complexation of the alkali metal by the epoxide oxygen. Reactions of Bu 4 AlLi and Et 4 AlNa with trans -ethyl 3-phenylglycidate produce the hydroxy esters resulting from an attack on the benzyl carbon of the epoxide bridge and with total inversion of its configuration. , …”

Section: Reactions Of Maas Involving Nucleophile Ligand Transfer Proc...mentioning

confidence: 99%

Mixed AggregAte (MAA): A Single Concept for All Dipolar Organometallic Aggregates. 2. Syntheses and Reactivities of Homo/HeteroMAAs

2013

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6. Conclusion 7706 Author Information 7706 Biographies 7707 Acknowledgment 7707 Abbreviations Used 7707 References 7708the corresponding allyl-and propargylchromium reagents that further react with a variety of electrophiles to afford the corresponding adducts in high yields. 102 Bu 6 CrLi 3 similarly behaves as a formal two-electron reductant with ketones and esters bearing a leaving group at the α-position to produce enolates that are intercepted with a variety of electrophiles with high selectivities (Table 8). 103 Such enolates are also capable of reacting with oxiranes to afford γand β-hydroxy esters, depending on the Lewis acid used as promoter. 2143.2.2. Two-Electron Transfers from M,Mn-HeteroMAAs (M = Li, MgX). In 1976, Cahiez et al. disclosed the possible reduction in THF of alkenyl bromides or iodides, as well as aryl chlorides or bromides, using i-PrMgCl in the presence of a catalytic amount of MnCl 2 . 215 The authors proposed the in situ formation of unstable i-Pr 3 MnMgCl and its decomposition by β-elimination to H 3 MnMgCl; reaction of the latter with the halide would then afford an unstable Mn(IV) intermediate, able Scheme 23 Scheme 24 Scheme 21 Scheme 22

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“…Although C−C bond formation at the C2 position has proved to be quite useful in the total synthesis of natural products, certain problems are incurred in the reactions using organocopper reagents: (1) the regioselectivity strongly depends on the structure of the substrates; (2) introduction of an alkynyl group seems to be extremely difficult because of the low reactivity of alkynylcopper reagents. The present Letter describes a new type of C2 selective nucleophilic substitution reaction of 2,3-epoxyalkanols using alkyl- and alkynylaluminum ate complexes …”

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confidence: 99%

Regioselective Alkyl and Alkynyl Substitution Reactions of Epoxy Alcohols by the Use of Organoaluminum Ate Complexes: Regiochemical Reversal of Nucleophilic Substitution Reactions

Sasaki

Tanino²,

Miyashita³

2001

Org. Lett.

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Unprecedented nucleophilic substitution reactions of 2,3-epoxy-1-alkanols with alkyl- and alkynylaluminum ate complexes have been studied and demonstrated to occur at the C2 position with extremely high stereoselectivity, i.e., with exactly reversed regioselectivity to that obtained in the substitution reactions by normal organoaluminum reagents, resulting in the formation of the C2-alkyl and C2-alkynyl substitution products in excellent yields.

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Stereoselectivite et regioselectivite de l'alkylation d'epoxydes par les “ates” complexes : Tetrabutylaluminate de lithium et tetraethylaluminate de sodium.

Cited by 21 publications

References 6 publications

Synthesis of Arborescent Isoprene Homopolymers

Synthesis of Arborescent Isoprene Homopolymers

Mixed AggregAte (MAA): A Single Concept for All Dipolar Organometallic Aggregates. 2. Syntheses and Reactivities of Homo/HeteroMAAs

Regioselective Alkyl and Alkynyl Substitution Reactions of Epoxy Alcohols by the Use of Organoaluminum Ate Complexes: Regiochemical Reversal of Nucleophilic Substitution Reactions

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