Rhodium catalysed enantioselective synthesis of mono-(halo)-methyl-cyclopropanes

The catalytic asymmetric synthesis of mono-fluoro-, -chloro- and -bromomethyl-1,2-diaryl cyclopropane ester is described. The reaction, using Rh₂((S)-BTPCP)₄ as a catalyst, allowed the formation of the desired cyclopropanes in good to excellent yields (up to 99%) and excellent diastereoselectivities (up to >20 : 1) and with a high level of enantioselectivities (up to 98% ee). Finally, the synthetic utility of the chiral cyclopropanes was also demonstrated.