Transition‐Metal‐Free Cascade Enyne Rearrangement and Cyclopropanation of Allenylphosphine Oxides with N‐Tosylhydrazones Accessing Alkynylcyclopropane Derivatives

We disclose an concise synthesis of alkynylcyclopropane derivatives containing adjacent quaternary carbon centers via a transition‐metal free cascade enyne rearrangement and cyclopropanation process. This methodology, started from a variety of allenylphosphine oxides and N‐tosylhydrazones, features the advantage of transition‐metal‐free, operational simplicity, wide substrate scope and good functional group tolerance.