Energy‐Transfer‐Enabled Skeletal Rearrangement of Cyclic Ketones into Strained Cyclopropane‐Fused Medium Rings

Abstract Cyclopropane‐fused medium rings (CFMR) are attractive structural motifs that combine high strain with unique three dimensionality, however their efficient and modular synthesis remains a formidable challenge. Herein, we present a general photocatalytic skeletal editing strategy that enables a direct topological leap—a single‐step reorganization that simultaneously alters both ring size and fusion topology—from readily available five‐ to eight‐membered cyclic ketones into diverse seven‐ to ten‐membered cyclopropane‐fused medium rings. This transformation proceeds through a novel energy‐transfer‐induced, diradical‐mediated 1,4‐carbonyl migration, orchestrating a “ring expansion–collapse” cascade to forge the strained bicyclic frameworks straightforward, which is supported by DFT calculations. This strategy features broad substrate scope, excellent functional‐group compatibility, and high efficiency, enabling the late‐stage diversification of complex molecules and exploration of CFMR chemical space that was previously inaccessible. Moreover, integration of this strategy with further skeletal modification enables rapid construction of versatile [n.3.0] bicycles.