Anionic Polymerization of Butadiene Initiated by Tributyltin Sodium. Kinetic Analysis of Induction Periods Generated by Transfer to Initiator Precursor

This article addresses the mechanistic features of asymmetric carbolithiation of β-methylstyrenes. While often the presence of functional groups is required to obtain high enantioselectivities in carbolithiation reactions, simple β-methylstyrene also gives high selectivities in (-)-sparteine-mediated addition of alkyl lithium compounds. Computational studies on the carbolithiation of β-methylstyrene with (-)-sparteine show that the observed selectivities are the result of repulsion effects in the diastereomeric transition states between the (-)-sparteine⋅alkyl lithium adduct and the β-methylstyrene, upon approximation of the two reactants. In contrast, for the ortho-amino β-methylstyrene (E)-benzyl(2-propenylphenyl)amine (4) X-ray structure analyses of intermediate lithium amides indicate a carbolithiation mechanism in which one side of the double bond is shielded by the amide moiety, leaving only one side free for approach of the chiral alkyl lithium adduct.

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Mechanistic Insight into Stereoselective Carbolithiation

Gessner

Koller

Strohmann

et al. 2011

Chemistry A European J

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Reactions of Sodium Diisopropylamide: Liquid-Phase and Solid–Liquid Phase-Transfer Catalysis by N,N,N′,N″,N″-Pentamethyldiethylenetriamine

Woltornist

Algera

et al. 2021

J. Am. Chem. Soc.

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Sodium diisopropylamide (NaDA) in N,N-dimethylethylamine (DMEA) and DMEA−hydrocarbon mixtures with added N,N,N′,N″,N″-pentamethyldiethylenetriamine (PMDTA) reacts with alkyl halides, epoxides, hydrazones, arenes, alkenes, and allyl ethers. Comparisons of PMDTA with N,N,N′,N′tetramethylethylenediamine (TMEDA) accompanied by detailed rate and computational studies reveal the importance of the trifunctionality and κ 2 −κ 3 hemilability. Rate studies show exclusively monomer-based reactions of 2-bromooctane, cyclooctene oxide, and dimethylresorcinol. Catalysis with 10 mol % PMDTA shows up to >30-fold accelerations (k cat > 300) with no evidence of inhibition over 10 turnovers. Solid−liquid phase-transfer catalysis (SLPTC) is explored as a means to optimize the catalysis as well as explore the merits of heterogeneous reaction conditions.

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Ketone Enolization with Sodium Hexamethyldisilazide: Solvent- and Substrate-Dependent E–Z Selectivity and Affiliated Mechanisms

Woltornist

Collum

2021

J. Am. Chem. Soc.

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Ketone enolization by sodium hexamethyldisilazide (NaHMDS) shows a marked solvent and substrate dependence. Enolization of 2-methyl-3-pentanone reveals E−Z selectivities in Et 3 N/toluene (20:1), methyl-t-butyl ether (MTBE, 10:1), N,N,N′,N″,N″-pentamethyldiethylenetriamine (PMDTA)/toluene (8:1), TMEDA/toluene (4:1), diglyme (1:1), DME (1:22), and tetrahydrofuran (THF) (1:90). Control experiments show slow or nonexistent stereochemical equilibration in all solvents except THF. Enolate trapping with Me 3 SiCl/Et 3 N requires warming to −40 °C whereas Me 3 SiOTf reacts within seconds. In situ enolate trapping at −78 °C using preformed NaHMDS/Me 3 SiCl mixtures is effective in Et 3 N/toluene yet fails in THF by forming (Me 3 Si) 3 N. Rate studies show enolization via mono-and disolvated dimers in Et 3 N/toluene, disolvated dimers in TMEDA, trisolvated monomers in THF/toluene, and free ions with PMDTA. Density functional theory computations explore the selectivities via the E-and Z-based transition structures. Failures of theory-experiment correlations of ionic fragments were considerable even when isodesmic comparisons could have canceled electron correlation errors. Swapping 2-methyl-3-pentanone with a close isostere, 2methylcyclohexanone, causes a fundamental change in the mechanism to a trisolvated-monomer-based enolization in THF.

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Anionic Polymerization of Butadiene Initiated by Tributyltin Sodium. Kinetic Analysis of Induction Periods Generated by Transfer to Initiator Precursor

Cited by 3 publications

References 14 publications

Mechanistic Insight into Stereoselective Carbolithiation

Mechanistic Insight into Stereoselective Carbolithiation

Reactions of Sodium Diisopropylamide: Liquid-Phase and Solid–Liquid Phase-Transfer Catalysis by N,N,N′,N″,N″-Pentamethyldiethylenetriamine

Ketone Enolization with Sodium Hexamethyldisilazide: Solvent- and Substrate-Dependent E–Z Selectivity and Affiliated Mechanisms

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