Asymmetric epoxidation using iminium salt organocatalysts featuring dynamically controlled atropoisomerism.

Introduction of a pseudoaxial substituent at a stereogenic center adjacent to the nitrogen atom in binaphthyl- and biphenyl-derived azepinium salt organocatalysts affords improved enantioselectivities and yields in the epoxidation of unfunctionalized alkenes. In the biphenyl-derived catalysts, the atropoisomerism at the biphenyl axis is controlled by the interaction of this substituent with the chiral substituent at nitrogen.