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Controlling the cross‐selectivity and diastereoselectivity in cross‐pinacol coupling reactions remains challenging. Herein, we report a redox‐neutral strategy that enables the cross‐selective pinacol coupling between pyridyl ketones and amine‐derived aldehydes with high diastereoselectivity. Under visible‐light irradiation in the presence of a samarium catalyst and visible‐light antenna ligand, the desired cross‐coupling products are obtained in up to 86% yield with >20:1 diastereomeric ratio. The observed selectivities originate from the formation of a samarium‐coordinated carbanion species derived from the ketone, which undergoes diastereoselective nucleophilic addition to an aldehyde generated via oxidation of the amine followed by hydrolysis. In addition, heterolytic CC bond cleavage of the homopinacol coupling product generates the carbanion species under samarium catalysis, thereby enhancing the cross‐selectivity.
Kuribara et al. (Mon,) studied this question.