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

Abstract

The asymmetric cyclopropanation of 1,1-diphenylethylene ( 2 ) with ethyl 3,3,3-trifluoro-2-diazopropionate ( 1 ) in the presence of chiral Rh(II) catalysts affords cyclopropane 3 with yields and enantioselectivities of up to 72 and 40%, respectively. Similar results are obtained for asymmetric cyclopropenation of hex-1-yne ( 4 ), although enantioselectivity is lower. The cyclopropanation of mono-substituted olefins ( 8a– 8e ) with 1 leads to cis/ trans-mixtures of cyclopropanes 9a– 9e with a maximum ee of 75% for 4-methoxystyrene ( 8c ).