Role of Additives to Overcome Limitations of Intermolecular Rhodium-Catalyzed Asymmetric Cyclopropanation

This study describes general methods for the enantioselective syntheses of disubstituted cyclopropane carboxylates including substitution patterns or heterocycle functionality previously observed as significant limitations. The key step is the dirhodium tetracarboxylate-catalyzed asymmetric cyclopropanation of vinyl arenes with aryl- or heteroaryldiazoacetates. The reactions are highly diastereoselective and high asymmetric induction could be achieved using either (R)-pantolactone as a chiral auxiliary or chiral dirhodium tetracarboxylate catalysts.