Development of Biisoquinoline-Based Chiral Diaminocarbene Ligands: Enantioselective S_N2‘ Allylic Alkylation Catalyzed by Copper−Carbene Complexes

Chiral biisoquinoline-based diaminocarbene ligands (BIQ) were designed to create a chiral environment extended toward the metal center, which was confirmed by an X-ray structure. The concise ligand synthesis is highlighted by a modified Bischler−Napieralski cyclization of bisamides prepared from readily available chiral phenethylamines, and allows easy variation of the stereodifferentiating groups. The cyclohexyl-BIQ−copper complex is an efficient catalyst for enantioselective SN2‘ allylic alkylation with Grignard reagents showing SN2‘ regioselectivity higher than 5:1 and enantioselectivity in the range of 68−77% ee.