[4 + 1] Cycloaddition Reaction of α,β-Alkynic Hydrazones and KSCN under Transition-Metal-Free Conditions: Synthesis of N-Iminoisothiazolium Ylides.

A novel heteroannulation reaction between α,β-alkynic hydrazones and potassium thiocyanate has been developed for the synthesis of N-iminoisothiazolium ylides. The transformation features wide substrate scope, functional tolerance, and easy operation. This investigation involves a [4 + 1]-type cycloaddition reaction and C-S/S-N bond formation under transition-metal-free conditions. The application of this transformation to the gram-scale preparation of the N-imide ylide is also accomplished.