Highly Stereoselective Positional Isomerization of Styrenes via Acid-Catalyzed Carbocation Mechanism

The first transition metal-free highly stereoselective positional isomerization of various α-alkyl styrenes through a carbocation mechanism triggered strategy is developed by using Al(OTf)₃ as a hidden Brønsted acid catalyst, which provides facile access to value-added acyclic tri- and tetra-substituted alkenes in good yields with high stereoselectivity under mild conditions. The practicality of this protocol is further highlighted by the gram-scale synthesis, high stereoselectivity, good functional group tolerance, and simple operation. Mechanistic studies support that Al(OTf)₃ acts as a hidden Brønsted acid catalyst and a carbocation intermediate is formed.