Asymmetric catalysis of intramolecular cyclopropanation of 5-aryl-1-diazo-1-mesitylsulfonyl-5-hexen-2-ones

We have examined the catalytic asymmetric intramolecular cyclopropanation (IMCP) reactions of 5-aryl-1-diazo-1-mesitylsulfonyl-5-hexen-2-ones, and found that the substituent of the 5-aryl group dramatically changes the enantioselectivity. That is, no enantioselectivity was observed when the substituent was a methoxy group; however, enantioselectivity was moderate when the substituent was a methylenedioxy group or a tert-butyldimethylsilyloxy group, and it dramatically increased when the substituent was lacking (96% ee) or a benzoyloxy group (93% ee).