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

The merger of open-shell and closed-shell organometallic chemistry steps has enabled multiple effective cross-coupling pathways. Here we report a visible-light promoted photoredox-cobalt catalyzed Minisci reaction of N-heteroarenes under mild and sustainable 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 in flow vs 0.02 mmol/h 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.