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Asymmetric allylic substitution–isomerization to axially chiral enamides via hydrogen-bonding assisted central-to-axial chirality transfer†

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Axially chiral enamides bearing a N–C axis have been recently studied and were proposed to be valuable chiral building blocks, but a stereoselective synthesis has not been achieved. Here, we… Click to show full abstract

Axially chiral enamides bearing a N–C axis have been recently studied and were proposed to be valuable chiral building blocks, but a stereoselective synthesis has not been achieved. Here, we report the first enantioselective synthesis of axially chiral enamides via a highly efficient, catalytic approach. In this approach, C(sp2)–N bond formation is achieved through an iridium-catalyzed asymmetric allylation, and then in situ isomerization of the initial products through an organic base promoted 1,3-H transfer, leading to the enamide products with excellent central-to-axial transfer of chirality. Computational and experimental studies revealed that the 1,3-H transfer occurs via a stepwise deprotonation/re-protonation pathway with a chiral ion-pair intermediate. Hydrogen bonding interactions with the enamide carbonyl play a significant role in promoting both the reactivity and stereospecificity of the stepwise 1,3-H transfer. The mild and operationally simple formal N-vinylation reaction delivered a series of configurationally stable axially chiral enamides with good to excellent yields and enantioselectivities.

Keywords: enamides via; central axial; transfer; chiral enamides; hydrogen bonding; axially chiral

Journal Title: Chemical Science
Year Published: 2020

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