Construction of 8–10 membered rings is achieved via a base-promoted two carbon ring expansion as a general strategy to formally insert a vinyl group to cyclic ketones.

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.