A new type of imido group donor: Synthesis and characterization of sulfonylimino-Δ³-bromane that acts as a nitrenoid in the aziridination of olefins at room temperature under metal-free conditions

A stable sulfonylimino-λ³-bromane, CF₃SO₂N^--Br⁺C₆H₄-p-CF₃, has been synthesized and structurally characterized for the first time. X-ray crystallographic analyses indicated a centrosymmetric dimer structure with little double-bond character for the "ylidic" Br-N bond. The iminobromane serves as an efficient imido group donor and directly undergoes aziridination of olefins stereospecifically with retention of original stereochemistry. Very interestingly, the aziridination proceeds at room temperature using limiting amounts of alkenes under transition-metal-free conditions. The observed rate constants for aziridination of cis-cyclooctene are proportional to concentration of the olefin. The results suggest the involvement of a bimolecular transition state, in which an olefin attacks the σ* N-Br orbital of iminobromane in the nitrenoid transfer process.