Enantioselective Synthesis of trans-Disubstituted Cyclopropyltrifluoroborate Building Blocks through Ru-Catalyzed Cyclopropanation

Enantioselective synthesis of trans-1,2-disubstituted cyclopropanes containing Lewis basic nitrogen functionalities remains a challenge to metal-catalyzed cyclopropanation reactions. Herein, we reported an alternative strategy to access similar products by a sequence of enantioselective cyclopropanation of potassium vinyltrifluoroborate, followed by cross-coupling of the cyclopropyl boronate product. The cyclopropanation process was readily performed in a 50 g scale from commercially available starting materials. An interesting enrichment of product enantiomeric purity by simple crystallization is also noted.