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

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.