Transannular 1,3-Addition of Cyclic Ethers via C-O Bond Cleavage Triggered by Low-Valent Phosphorus.

By employing a spatially constrained strategy, we have altered the reaction behavior between phosphinidene and alkynes, triggering a 1,3-addition of cyclic ethers to a zwitterionic phosphindole intermediate. This work provides a facile route to otherwise inaccessible cyclophanes and reveals the extraordinary reactivity of zwitterionic phosphindole toward the C-O bond of cyclic ethers. Moreover, the distinct reactivity of the zwitterionic intermediate revealed by this work could have implications for main-group element-mediated σ bond activation.