Enantioselective synthesis of atropisomeric indoles via iron catalysed oxidative cross-coupling

04 August 2021, Version 2
This content is a preprint and has not undergone peer review at the time of posting.

Abstract

Heterobiaryl compounds that exhibit axial chirality are of increasing value and interest across several fields, but direct oxidative methods for their enantioselective synthesis are elusive. Here we disclose that an iron catalyst in the presence of a chiral PyBOX ligand and an oxidant enables direct coupling between naphthols and indoles to yield atropisomeric heterobiaryl compounds with high levels of enantioselectivity. The reaction exhibits remarkable chemoselectivity and exclusively yields cross-coupled products without competing homocoupling. Mechanistic investigations enable us to postulate that an indole radical is generated in the reaction but that this is likely an off-cycle event, and that the reaction proceeds through formation of a chiral Fe-bound naphthoxy radical which is trapped by a nucleophilic indole. We envision that this simple, cheap, and sustainable catalytic manifold will facilitate access to a range of heterobiaryl compounds and enable their applications across the fields of materials science, medicinal chemistry, and catalysis.

Keywords

atropisomer
catalysis
oxidative cross-coupling
enantioselective
iron

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