Asymmetric Anion-π Catalysis of Iminium/Nitroaldol Cascades To Form Cyclohexane Rings with Five Stereogenic Centers Directly on π-Acidic Surfaces

Anion-pi interactions have been introduced to catalysis only recently, and evidence for their significance is so far limited to one classical model reaction in enolate and enamine chemistry. In this report, asymmetric anion-pi catalysis is achieved for the first time for a more demanding cascade process. The selected example affords six-membered carbocycles with five stereogenic centers in a single step from achiral and acyclic substrates. Rates, yields, turnover, diastereo- and enantioselectivity are comparable with conventional catalysts. Rates and stereoselectivity increase with the pi-acidity of the new anion-pi catalysts. Further support for operational anion-pi interactions in catalysis is obtained from inhibition with nitrate. As part of the stereogenic cascade reaction, iminium chemistry and conjugate additions are added to the emerging repertoire of asymmetric anion-pi catalysis.