Metal-Free Radical [3 + 2] Annulation of Tetraalkylthiuram Disulfide with Alkynes/Alkenes: An Approach of Synthesizing 1,3-Dithiole and 1,3-Ditholane Derivatives.

A novel and metal-free [3 + 2] annulation of tetraalkylthiuram disulfide with alkynes/alkenes has been developed using Selectfluor at room temperature. The formed 1,3-dithiol-2-ylium/1,3-dithiolan-2-ylium salts can be easily transformed into the corresponding 1,3-dithiol-2-ylidenes/1,3-ditholan-2-ylidenes by one-pot subsequent condensation with malononitrile. The present protocol features the use of easily accessible starting materials, mild reaction conditions, good tolerance with diverse functional groups, easy scale-up, and a wide substrate scope, affording the desired products in good yields.