Thiophane‐Catalyzed Umpolung of N‐Bromoimides for Dibromination of Olefins

A thiophane‐catalyzed dibromination of olefins using NBS as the sole bromine source has been developed, providing a low‐cost and mild methodology for preparing vicinally dibrominated compounds from electron‐neutral or ‐deficient alkenes. The mechanistic investigation showed that 2,3‐dihydrothiophene generated in situ from the reaction of thiophane with NBS was the actual catalyst, which reversed the polarity of NBS to yield bromide ion.