Acceleration of Inward Ring Opening of 3‐Phosphorylcyclobutenes

3‐Phosphorylcyclobutenes undergo a 4π‐electrocyclic ring opening reaction faster than cyclobutene itself, and afford the corresponding 1,3‐dienes with the cis isomer predominating. The accelerating effect and the inward preference of the phosphonate substituents are ascribed to the orbital interaction between the breaking C−C σ‐orbital of the cyclobutene backbone with the P−O σ* orbitals at the transition state. Phaster with Phosphorus! 3‐Phosphorylcyclobutenes undergo a 4π‐electrocyclic ring opening reaction faster than cyclobutene itself, affording the corresponding 1,3‐dienes, with the cis isomer predominating.