NMR investigation of asymmetric conjugate additions using chiral 4-phenyloxazolidinone as a mechanistic probe

Bill Show Lou, Guigen Li, Feng Di Lung, Victor J Hruby

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Abstract

The asymmetric conjugate addition of organocopper(I) reagents to α,β-unsaturated N-acyl-4-phenyl-2-oxazolidinones has been studied by 1H- and 13C-NMR spectroscopy using the Evans-type 4-phenyloxazolidinone auxiliary as a mechanistic probe. Three chiral intermediates were observed directly. The two metal methyl groups in the olefin-copper(I) complex 2, which is crucial for asymmetric induction, were assigned by both chemical shift and kinetic analysis. The dihedral angle of the α- and β-protons of the metallo enolate 3 was measured as 150° which provided valuable information for examining the stereochemical effects of the β position on the chirality of the α center. Enolates 3 and 4 are reversibly temperature dependent. Enolate 3 is the major component at 253 K, while enolate 4 becomes the major component at 293 K. Therefore, temperatures lower than ∼253 K are required for high stereoselectivity in the electrophilic bromination of the resulting enolate to build an a-chiral center. The free energy of activation (ΔG) and rate constant (kc) of the equilibrium were measured as 15.0 kcal/mol and 1.4 × 102 s-1, respectively.

Original languageEnglish (US)
Pages (from-to)5509-5514
Number of pages6
JournalJournal of Organic Chemistry
Volume60
Issue number17
StatePublished - 1995

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Nuclear magnetic resonance
Oxazolidinones
Stereoselectivity
Chirality
Chemical shift
Alkenes
Dihedral angle
Reaction kinetics
Nuclear magnetic resonance spectroscopy
Free energy
Protons
Copper
Rate constants
Metals
Chemical activation
Temperature

ASJC Scopus subject areas

  • Organic Chemistry

Cite this

NMR investigation of asymmetric conjugate additions using chiral 4-phenyloxazolidinone as a mechanistic probe. / Lou, Bill Show; Li, Guigen; Lung, Feng Di; Hruby, Victor J.

In: Journal of Organic Chemistry, Vol. 60, No. 17, 1995, p. 5509-5514.

Research output: Contribution to journalArticle

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N2 - The asymmetric conjugate addition of organocopper(I) reagents to α,β-unsaturated N-acyl-4-phenyl-2-oxazolidinones has been studied by 1H- and 13C-NMR spectroscopy using the Evans-type 4-phenyloxazolidinone auxiliary as a mechanistic probe. Three chiral intermediates were observed directly. The two metal methyl groups in the olefin-copper(I) complex 2, which is crucial for asymmetric induction, were assigned by both chemical shift and kinetic analysis. The dihedral angle of the α- and β-protons of the metallo enolate 3 was measured as 150° which provided valuable information for examining the stereochemical effects of the β position on the chirality of the α center. Enolates 3 and 4 are reversibly temperature dependent. Enolate 3 is the major component at 253 K, while enolate 4 becomes the major component at 293 K. Therefore, temperatures lower than ∼253 K are required for high stereoselectivity in the electrophilic bromination of the resulting enolate to build an a-chiral center. The free energy of activation (ΔG†) and rate constant (kc) of the equilibrium were measured as 15.0 kcal/mol and 1.4 × 102 s-1, respectively.

AB - The asymmetric conjugate addition of organocopper(I) reagents to α,β-unsaturated N-acyl-4-phenyl-2-oxazolidinones has been studied by 1H- and 13C-NMR spectroscopy using the Evans-type 4-phenyloxazolidinone auxiliary as a mechanistic probe. Three chiral intermediates were observed directly. The two metal methyl groups in the olefin-copper(I) complex 2, which is crucial for asymmetric induction, were assigned by both chemical shift and kinetic analysis. The dihedral angle of the α- and β-protons of the metallo enolate 3 was measured as 150° which provided valuable information for examining the stereochemical effects of the β position on the chirality of the α center. Enolates 3 and 4 are reversibly temperature dependent. Enolate 3 is the major component at 253 K, while enolate 4 becomes the major component at 293 K. Therefore, temperatures lower than ∼253 K are required for high stereoselectivity in the electrophilic bromination of the resulting enolate to build an a-chiral center. The free energy of activation (ΔG†) and rate constant (kc) of the equilibrium were measured as 15.0 kcal/mol and 1.4 × 102 s-1, respectively.

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