Phosphoryl-Deoxygenated Access to Cationic Phosphacycles Enabled by Intramolecular SEAr process of Pentavalent Phosphorus Cations

Achieving a direct functionalization of phosphine oxides through the cleavage of the inert P=O double bond remains a formidable challenge in phosphorus chemistry. Herein, we reported a metal-free catalytic electrophilic aromatic substitution (SEAr) phosphacyclization, effectively transforming phosphine oxides into valuable cationic phosphacycles by introducing a powerful nucleofugality (-OTf) to promote the SEAr process via a formal P(v)-dication transition-state. Meanwhile, the theoretically calculated results indicate that the splitting P─OTf bond is pivotal to trigger the SEAr reaction of P(v)-cationic species. Moreover, the kinetic studies also verify that the generated acid (HOTf) would facilitate the nucleofugality leaving from the cationic P-center to accelerate the cyclization. In addition, we investigated their photophysical and electrochemical properties of some typical phosphacycles, which implied the fused di-cationic phosphacyles could be a class of potential optical function molecules. Summarily, this work not only extends the application boundary of phosphine oxides but also paves a way for effectively preparing various mono/di/tri-cationic phosphacycles.