Construction of Medium‐Sized Rings Enabled by a Base‐Mediated Ring Expansion Reaction

Medium‐sized ring architectures, widely present in natural products and small molecular drugs, are challenging synthetic targets. Herein, a base‐promoted two‐carbon ring expansion is described as a general strategy to formally insert a vinyl group to cyclic ketones. This method efficiently constructs a wide range of fused‐medium‐sized (8–10‐membered) ring systems and successfully applies to the late‐stage skeleton editing of complex natural products. Notable features of the procedure include readily available materials, wide substrate scope, and mild conditions.