Highly Selective Synthesis of Spirocyclobutanes via [2 + 2] Cycloaddition of α,β‐Unsaturated Acenaphthenone and Acenaphthylene

The cyclobutane framework serves as an important class of rigid scaffolds with broad applications in medicinal chemistry and advanced materials. In particular, spirocyclobutanes have emerged as a key pharmacophore in numerous bioactive molecules owing to their distinctive three‐dimensional geometry and enhanced metabolic stability. Herein, we report an efficient and practical synthetic strategy that constructs the spirocyclobutane core in a single step via a visible‐light‐promoted, copper sulfate‐catalyzed intermolecular [2 + 2] cycloaddition between α,β‐unsaturated acenaphthenones and acenaphthylene. This operationally simple protocol requires only straightforward filtration to afford products in high purity. Meanwhile, the good functional group tolerance and broad substrate scope were well demonstrated by delivering the diverse target spirocyclobutanes in moderate to excellent yields (50%–92%) with high stereoselectivity. This novel method thus offers a practical, economical, and sustainable alternative for the construction of spirocyclobutane derivatives.