Photocatalytic Strain-Release Transformation of Bicyclo[1.1.0]butanes (BCB) Using Strategically Tuned Covalent Organic Frameworks

We designed and synthesized crystalline, porous, covalent organic framework (COF) photocatalysts featuring highly stabilized valence band edges to promote facile charge transport, active site accessibility, and delayed electron–hole recombination. These COFs enabled the photocatalytic strain-release Minisci reaction of bicyclo[1.1.0]butane (BCB) for the direct synthesis of N -heteroarene-functionalized spiro-cyclobutyl oxindoles. The transformation operates through halogen-atom transfer (XAT) mediated by α-aminoalkyl radicals generated via photocatalytic oxidation of alkyl amines. This strategy permits rapid access to structurally diverse spirocyclic scaffolds, including those bearing all-carbon quaternary centers, and facilitates late-stage functionalization of N -heteroarene-containing bioactive molecules and natural products. The heterogeneous COF catalysts exhibit exceptional recyclability, retaining full activity over eight consecutive cycles. Detailed mechanistic investigations, including control reactions, photophysical measurements, and electrochemical studies, provide insight into the reaction pathway.