Cascades of Interrupted Pummerer Reaction-Sigmatropic Rearrangement.

A new class of Pummerer chemistry has emerged as a powerful tool in organic synthesis. The new technology consists of a beautiful cascade of an interrupted Pummerer reaction and the subsequent [3,3] sigmatropic rearrangement. The interrupted Pummerer reactions of alkenyl or aryl sulfoxides with unsaturated nucleophiles such as allylic silanes, ketones, and phenols provide sulfonium intermediates, which are ready to undergo smooth charge-accelerated [3,3] sigmatropic rearrangement with excellent to exclusive regioselectivity. Some of the transformations proceed with transient loss of aromaticity. The reactions afforded five-membered heterocycles, benzofurans, and biaryls of importance, depending on the sulfoxides and nucleophiles used. The reactions are unique and game-changing because they are efficient, robust, redox-neutral, regioselective, and metal-free, which perfectly fits the need of modern organic synthesis. This chemistry also underscores the synthetic potential of organosulfur chemistry.