Photocatalytic Two-Carbon Skeletal Expansion of Cyclic Alcohols to Cycloalkenes

Abstract

A unified strategy for accessing substituted cycloalkenes via two-carbon ring expansion of cycloalkanols is described. Organophotocatalyzed oxidation of cycloalkanols, proceeding either via direct oxidation or via proton-coupled electron transfer (PCET), is sequentially coupled with intramolecular Wittig olefination. This process converts previously unexplored ketone intermediates into valuable cycloalkenes across a broad substrate scope and in high yields. The post-synthetic diversification of the products serves as a synthetic handle for downstream manipulations, thus offering opportunities to build up many complex molecular architectures. Combined experimental studies support a sequential mechanism involving radical ring fragmentation-addition followed by ionic Wittig olefination, affording the desired cycloalkene derivatives.