A new class of reagents is described for C-H functionalization by means of C-H insertion using donor/acceptor-substituted rhodium(II) carbene intermediates. The 2,2,2-trichloroethyl aryl and heteroaryl diazoacetates, together with the dirhodium triarylcyclopropane carboxylate catalyst Rh2(R-BPCP)4, enabled the enantioselective intermolecular C-H functionalization of a range of methyl ethers with high levels of site selectivity and enantioselectivity.

The rhodium-catalyzed reaction of electron-deficient alkenes with substituted aryldiazoacetates and vinyldiazoacetates results in highly stereoselective cyclopropanations. With adamantylglycine derived catalyst Rh2(S-TCPTAD)4, high asymmetric induction (up to 98% ee) can be obtained with a range of substrates. Computational studies suggest that the reaction is facilitated by weak interaction between the carbenoid and the substrate carbonyl but subsequently proceeds via different pathways depending on the nature of the carbonyl.. Acrylates and acrylamides result in the formation of cyclopropanation products while the use of unsaturated aldehydes and ketones results in the formation of epoxides.

Achieving selective C–H functionalization is a significant challenge that requires discrimination between many similar C–H bonds.