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The asymmetric Simmons-Smith reaction is a cyclopropanation where a carbenoid (intermediate zinc-iodine complex) reacts with an alkene to from a stereospecific cyclopropane via a cheletropic reaction. The oxygen atoms of the dioxaborolane ligand, along with the hydroxyl group of the alkene reagent, coordinate with the Zn atom anchoring the complex into a postion where only one stereoisomer can be formed.

Animations based on Wang, T; Liang. Y; Yu, ZX, J, Am. Chem. Soc. 133 (2011) pp. 9343-9353