Merging dual photoredox/cobalt catalysis and boronic acid (derivatives) activation for the Minisci reaction

Abstract

The merger of photoredox catalysis and organometallic chemistry has effectively enabled multiple cross-coupling pathways. Here we report a visible-light promoted photoredox-cobalt catalyzed Minisci reaction of N-heteroarenes under mild conditions, employing various boronic acids and derivatives as alkyl radical precursors. This study demonstrates the prominent ability of the Co co-catalyst to promote the oxidation step of the photocatalytic cycle following a reductive quenching pathway, thus avoiding the use of stoichiometric (inorganic) oxidants. This feature enables the straightforward application of photo-flow conditions, particularly attractive for an easy scale-up and to enhance the efficiency of the reaction (throughput: 0.78 mmol·h⁻¹ in flow vs. 0.02 mmol·h⁻¹ in batch). Furthermore, the process is predominantly selective towards the C2-alkylation of quinolines and a mechanistic rationale has been provided with both experimental and DFT calculation support. The developed protocol demonstrates broad applicability for the alkylation of different N-heteroarenes under suitable homogeneous conditions for a flow-compatible Minisci reaction.