Tetracoordinated boron species generated from the complexation of organoboron compounds with bases are highly important intermediates in molecular fragments coupling. The type of base significantly impacts both the reaction activity and mechanism of organoboron compounds. Herein, our structural and mechanistic insights show that the full heterolytic cleavage of the C−B bond in benzylic boronates, leading to the formation of benzyl potassium species, can be achieved by increasing the amount of alkoxides. This, in turn, significantly enhances the nucleophilicity of both secondary and tertiary benzylic boronates. This mechanistic insight has proven valuable in the divergent construction of C(sp3)−C(sp3 or sp2) and other C−X bonds (X = Si, Ge, Sn, S, Se), as demonstrated through the integration of base-catalyzed silylboration/diborylation reactions. Through machine-learning-assisted screening of approximately 104 substrate combinations, we have expanded the scope of electrophiles for this transformation to include challenging aromatic heterocycles. Moreover, the synthetic potential of this protocol was demonstrated through the construction of drug-relevant molecules that contain 1,1-diaryl pharmacophores.

The mechanisms of direct deoxygenative borylation of acetone and benzaldehyde with bis(catecholato)diborane (B2cat2) in the solvent N,N‐dimethylacetamide (DMA) are investigated through detailed density functional theory calculations. These calculations show that the isomer 1,2‐B2cat2 in situ generated from 1,1‐B2cat2 induced by DMA is the reactive boron intermediate for the reactions. The addition of the B−B bond of 1,2‐B2cat2 to the C=O bond of acetone or benzaldehyde via a concerted [2σ+2π]‐cycloaddition‐like transition state is the rate‐limiting step for both the triboration reaction of acetone and the monoboration reaction of benzaldehyde. DMA not only acts as the solvent but also promotes the structural isomerization of B2cat2, the deoxygenation of acetone to form the vinyl boronate intermediate and subsequent diboration of vinyl boronate with 1,2‐B2cat2, as well as the protodeboronation of the gem‐diboronate intermediate in the deoxygenative borylation of benzaldehyde. The presented computational results can explain the observed experimental facts and provide insight into the roles of the isomeric 1,2‐B2cat2 and the solvent DMA in related reactions.