Double-Stereodifferentiation in Rhodium-Catalyzed [2 + 2 + 2] Cycloaddition: Chiral Ligand/Chiral Counterion Matched Pair.

The first enantioselective metal-catalyzed [2 + 2 + 2] cycloaddition involving a double asymmetric induction has been devised. It relies on the use of an in situ generated chiral cationic rhodium(I) catalyst with a matched chiral ligand/chiral counterion pair. Careful optimization of the catalytic system, as well as of the reaction conditions, led to atroposelective [2 + 2 + 2] pyridone cycloadducts with high ee's up to 96%. This strategy outperformed those previously described involving a chiral ligand only or a chiral counterion only.