Chromium(II)-Catalyzed Diastereoselective and Chemoselective Csp2-Csp3 Cross-Couplings Using Organomagnesium Reagents

A simple protocol for performing chromium catalyzed highly diastereoselective alkylations of arylmagnesium halides with cyclohexyl iodides at ambient temperature has been developed. Furthermore, this ligand-free CrCl2 enables efficient electrophilic alkenylations of primary, secondary, and tetiary alkylmagnesium halides with readily available alkenyl acetates. Moreover, this chemoselective C-C coupling reaction with stereodefined alkenyl acetates proceeds in a stereoretentive fashion. A wide range of functional groups on alkyl iodides and alkenyl acetates are well tolerated, thus furnishing functionalized Csp(2)-Csp(3) coupling products in good yields and high diastereoselectivity. Detailed mechanistic studies suggest that the in situ generated low-valent chromium(I) species might be the active catalyst for these Csp(2)-Csp(3) cross-couplings.