CO₂ Unlocks Reactivity: Boryl Silyl Ketene Acetals Enable Mild and Direct C═C Bond Cleavage

Boron-ligand cooperation (BLC) has emerged as a powerful principle of bond activation with main-group elements, yet pyridine-based systems have so far eluded experimental evidence of CO₂ activation. We show here that four-membered pyridyl-boracycles activate CO₂ through a dearomatizing boron-carbon bond cleavage, unambiguously proceeding by a BLC rather than a B/N-FLP-type mechanism, as confirmed by density functional theory (DFT) studies, in contrast to previously predicted computational pathways. This process furnishes boryl silyl ketene acetals, a hitherto unknown class of enolate equivalents in which the two oxygen atoms are differentiated by boryl and silyl substituents. These intermediates exhibit remarkable follow-up reactivity, eventually leading to a mild, one-step C═C double-bond cleavage that delivers fulvene derivatives under additive-free conditions, thereby constituting an unprecedented form of metathesis. Overall, our findings establish boryl silyl ketene acetals derived from CO₂ as a novel class of main-group systems that unlock a reactivity platform with far-reaching synthetic implications.