Enantioselective synthesis of functionalized nitrocyclopropanes by organocatalytic conjugate addition of bromonitroalkanes to alpha,beta-unsaturated enones.

A general enantioselective synthesis of functionalized nitrocyclopropanes by organocatalytic conjugate addition of a variety of bromonitroalkanes to alpha,beta-unsaturated enone systems is presented. The process, efficiently catalyzed by the salts of 9-amino-9-deoxyepiquinine 1 d serves as a powerful approach to the preparation of synthetically and biologically important cyclopropanes with high levels of enantio- and diastereoselectivities. Since only 0.6 equivalents of bromonitromethane are used as a reagent, (S)-2 e is obtained enantiomerically pure by employing chiral 1 d as a highly efficient catalyst for its kinetic resolution (97 % ee at 51 % conversion, selectivity s=120).