Rotational Isomers of N-Methyl-N-arylacetamides and Their Derived Enolates: Implications for Asymmetric Hartwig Oxindole Cyclizations
摘要:
The rotational preferences of N-(2-bromo-4,6-dimethylphenyl)-N-methyl 2-phenylpropanamide were studied as a model of precursors for Hartwig asymmetric oxindole cyclizations. The atropisomers of this compound were separated by flash chromatography, and then the enantiomers were resolved and the interconversions of the stereocenter and the N-Ar axis were studied. Under thermal conditions, the axis is very stable. Under the basic conditions of the Hartwig cyclization, both the stereocenter and the chiral axis equilibrate via enolate formation. The N-Ar rotation barrier of a 2-phenylacetamide analogue was reduced from 31 kcal mol(-1) in the precursor to 17 kcal mol(-1) in the enolate. Reasons for this dramatic barrier reduction and implications of both N-Ar and amide C-N rotations for Hartwig cyclizations are discussed.
Rotational Isomers of N-Methyl-N-arylacetamides and Their Derived Enolates: Implications for Asymmetric Hartwig Oxindole Cyclizations
摘要:
The rotational preferences of N-(2-bromo-4,6-dimethylphenyl)-N-methyl 2-phenylpropanamide were studied as a model of precursors for Hartwig asymmetric oxindole cyclizations. The atropisomers of this compound were separated by flash chromatography, and then the enantiomers were resolved and the interconversions of the stereocenter and the N-Ar axis were studied. Under thermal conditions, the axis is very stable. Under the basic conditions of the Hartwig cyclization, both the stereocenter and the chiral axis equilibrate via enolate formation. The N-Ar rotation barrier of a 2-phenylacetamide analogue was reduced from 31 kcal mol(-1) in the precursor to 17 kcal mol(-1) in the enolate. Reasons for this dramatic barrier reduction and implications of both N-Ar and amide C-N rotations for Hartwig cyclizations are discussed.
Asymmetric synthesis of axially chiral anilides by Pd-catalyzed allylic substitutions with P/olefin ligands
作者:Yilin Liu、Xiangqing Feng、Haifeng Du
DOI:10.1039/c4ob01087f
日期:——
synthesis of axiallychiral anilides is therefore of great interest in synthetic and pharmaceutical chemistry. In this paper, a palladium-catalyzed asymmetric allylic substitution of ortho-substituted anilides using phosphorus amidite–olefin ligands was successfully achieved to afford a variety of axiallychiral anilides in high yields with up to 84% ee. The absolute configurations of chiral anilides were
Rotational Isomers of <i>N</i>-Methyl-<i>N</i>-arylacetamides and Their Derived Enolates: Implications for Asymmetric Hartwig Oxindole Cyclizations
作者:Jérémie Mandel、Xiaohong Pan、E. Ben Hay、Steven J. Geib、Craig S. Wilcox、Dennis P. Curran
DOI:10.1021/jo400385t
日期:2013.4.19
The rotational preferences of N-(2-bromo-4,6-dimethylphenyl)-N-methyl 2-phenylpropanamide were studied as a model of precursors for Hartwig asymmetric oxindole cyclizations. The atropisomers of this compound were separated by flash chromatography, and then the enantiomers were resolved and the interconversions of the stereocenter and the N-Ar axis were studied. Under thermal conditions, the axis is very stable. Under the basic conditions of the Hartwig cyclization, both the stereocenter and the chiral axis equilibrate via enolate formation. The N-Ar rotation barrier of a 2-phenylacetamide analogue was reduced from 31 kcal mol(-1) in the precursor to 17 kcal mol(-1) in the enolate. Reasons for this dramatic barrier reduction and implications of both N-Ar and amide C-N rotations for Hartwig cyclizations are discussed.