A Stereodivergent Approach to the Synthesis of gem-Diborylcyclopropanes.

We report a designed stereodivergent strategy for the synthesis of gem-diborylcyclopropanes. The reaction provides a highly modular approach to prepare cyclopropane ring variants bearing gem-(Bpin,Bpin), gem-(Bpin,Bdan), and gem-(Bpin,BF 3 K), with outstanding levels of stereocontrol. This was achieved by diastereoselective Pd-catalyzed cyclopropanation reactions of gem-diborylalkenes with α-diazoarylacetates and α-diazoaryl-trifluoromethyl. The key to the success of this general protocol was the diastereoselective trifluorination reaction of gem-diborylcyclopropanes, followed by the stereospecific interconversion of the trifluoroborate salts into the Bdan group.