Methyl carbenoid asymmetric cyclopropanation with

The cyclopropanation utilizing donor/acceptor rhodium carbenoids can be extended to a range of monosubstituted alkenes, occurring with very high asymmetric induction (Tab. 14.4) [40]. Reactions with electron-rich alkenes, where low enantioselectivity was observed at room temperature, could be drastically improved using the more hydrocarbon-soluble Rh2(S-DOSP)4 catalyst at -78°C. The highest enantioselectivity is obtained when a small ester group such as a methyl ester is used [40], a trend which is the opposite to that seen with the unsubstituted diazoacetate system [16]. 

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