C-H activation and functionalization of pyridinoid azines is a key transformation for the synthesis of many natural products, pharmaceuticals, and materials. Reflecting the azinyl nitrogen lone-pair steric repulsion, ability to irreversibly bind to metal ion catalysts, and the electron-deficient nature of pyridine, C-H functionalization at the important a-position remains challenging. Thus, the development of earth-abundant catalysts for the a-selective mono-functionalization of azines is a crucial hurdle for modern chemical synthesis. Here, the selective organolanthanide-catalyzed a-mono-borylation of a diverse series of pyridines is reported, affording a valuable precursor for cross-coupling reactions. Experimental and theoretical mechanistic evidence support the formation of a C-H activated η2-lanthanide-azine complex, followed by intermolecular a-mono-borylation via σ-bond metathesis. Notably, varying the lanthanide identity and substrate electronics promotes chemodivergence of the catalytic selectivity: smaller/more electrophilic lanthide3+ ions and electron-rich substrates favor selective a-C-H functionalization, whereas larger/less electrophilic lanthanide3+ ions and electron-poor substrates favor selective B-N bond-forming 1,2-dearomatization. Such organolanthanide series catalytic chemodivergence is, to our knowledge, unprecedented and relevant to placement of early lanthanides in the Periodic Table.

Chemodivergent organolanthanide catalyzed C-H a-mono-borylation of azines

ACS Spring 2022

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