Selective Synthesis of N‑Cyano Sulfilimines by Dearomatizing Stable Thionium Ions

For the selective synthesis of N-cyano sulfilimines, we have developed a new method based on the soft–soft interaction between thionium ion electrophiles and cyanonitrene nucleophiles. The stable thionium ion was successfully obtained by oxidative dearomatization using phenyliodine (III) diacetate (PIDA) in N,N-dimethylformamide (DMF). The sulfur imination reactions were tolerant to a wide range of functional groups and exhibited high selectivities and excellent yields. The existence of thionium ion intermediates was confirmed by ultraviolet/visible (UV/vis) spectroscopy and ¹H NMR experiments.