Enriching Alkene syn-Dihalogenation: Aryl Alkene, Bromine, Regio-Reversion, and Stereoconvergency

Alkene dihalogenation is widely utilized for organohalide synthesis as an indispensable synthetic tool. Ironically, the nearly perfect anti-diastereospecificity becomes a formidable hurdle when the other syn-diastereochemical course is desired. Thus, accessing the uncharted half of the stereochemical space has been an intriguing synthetic challenge. Despite the recent advancements in syn-dihalogenation, critical problems still remain to be resolved, such as the notorious unsuitability of aryl alkenes and low stereospecificity of dibromination. Herein, both of these issues are successfully addressed via our vicinal double electrophilic activation strategy to enable the development of a highly stereoselective syn-dibromination of aryl alkenes for the first time. Moreover, the use of two different halogens leads to unusual site-selectivity that is inaccessible via traditional methods. Furthermore, the complementary behavior of the alkene geometrical isomers allows for a rare type of stereoconvergent dibromination from E/Z mixtures. As a result, our work provides a number of enriching features to this promising research field.