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Asymmetric Barton–Zard Reaction To Access 3-Pyrrole-Containing Axially Chiral Skeletons

Research paper by Xiao-Long He, Hui-Ru Zhao, Xue Song, Bo Jiang, Wei Du, Ying-Chun Chen

Indexed on: 17 Apr '19Published on: 04 Apr '19Published in: ACS Catalysis



Abstract

Developing an efficient and reliable catalytic protocol to access atropisomeric compounds, especially those bearing five-membered heteroaryl structures with lower rotation barriers, is a challenging task. Here, we disclose an unprecedented atropenantioselective Barton–Zard reaction via a central-to-axial chirality transfer strategy, by employing α-substituted nitroolefins with a β-ortho-substituted (hetero)aryl group and α-isocyano substrates with various electron-withdrawing groups, under the catalysis of Ag2O and a cinchona-derived phosphine ligand, providing a robust approach to construct axially chiral 3-(hetero)aryl pyrroles with a substantial skeleton and functionality versatility. An alternative asymmetric phase transfer catalysis protocol was also demonstrated to be practical for the direct construction of axially chiral bisphosphine dioxides. In addition, good conformational stability is generally observed for the obtained atropisomers, and their potential application as valuable organocatalysts has been well demonstrated in a highly stereoselective formal [4 + 2] cycloaddition reaction.

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