LAUSR

N-Heterocyclic carbene (NHC) catalyzed desymmetrizing reactions of olefins have rapidly developed in recent years; however, the origins of the chemo- and stereoselectivities of these reactions remain poorly understood. Herein, we propose a mechanistic map for these reactions to predict how chemo- and stereoselectivities are controlled by different active intermediates (i.e., Breslow and acylazolium intermediates). Remarkably, our findings contradict a previous proposition that product structures are determined by a transformation between a pair of isomers.