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Achiral Counterion Control of Enantioselectivity in a Brønsted Acid-Catalyzed Iodolactonization
- Dobish, Mark C., Johnston, Jeffrey N.
- Journal of the American Chemical Society 2012 v.134 no.14 pp. 6068-6071
- carboxylic acids, catalysts, enantiomers
- Highly enantioselective halolactonizations have been developed that employ a chiral proton catalyst–N-iodosuccinimide (NIS) reagent system in which the Brønsted acid is used at catalyst loadings as low as 1 mol %. An approach that modulates the achiral counterion (equimolar to the neutral chiral ligand–proton complex present at low catalyst loadings) to optimize the enantioselection is documented for the first time in this transformation. In this way, unsaturated carboxylic acids are converted to γ-lactones in high yields (up to 98% ee) using commercially available NIS.