Asymmetric Catalysis on the Intramolecular Cyclopropanation of α-Diazo-β-keto Sulfones

This work describes the development of a highly enantioselective asymmetric catalysis on the intramolecular cyclopropanation of α-diazo-β-keto sulfones. We have found that the catalytic asymmetric intramolecular reactions of α-diazo-β-keto sulfones generally proceed with high enantioselectivity when the α-diazo-β-keto mesityl sulfone is used with the newly prepared ligand 2e. The absolute configuration of products has been determined by X-ray crystallographic analysis, and the outcome of the enantioselectivities is explained well by our proposed models A and B. The products possess great potential for natural product synthesis because (1) many different chemistries of cyclopropane, ketone, and sulfone are available, and (2) the products are generally highly crystalline, facilitating the supplies of enantiomerically pure synthetic intermediates.