Rh(II)-Catalyzed asymmetric carbene transfer with ethyl 3,3,3-trifluoro-2-diazopropionate

The asymmetric cyclopropanation of 1,1-diphenylethylene () with ethyl 3,3,3-trifluoro-2-diazopropionate () in the presence of chiral Rh(II) catalysts affords cyclopropane with yields and enantioselectivities of up to 72 and 40%, respectively. Similar results are obtained for asymmetric cyclopropenation of hex-1-yne (), although enantioselectivity is lower. The cyclopropanation of mono-substituted olefins () with leads to cis/trans-mixtures of cyclopropanes with a maximum ee of 75% for 4-methoxystyrene ().