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.