Copper-Catalyzed Enantioselective Boron Conjugate Addition: DFT and AFIR Study on Different Selectivities of Cu(I) and Cu(II) Catalysts

Abstract

We present a mechanistic survey on the LCu-catalyzed (L = chiral 2,2′-bipyridine ligand) enantioselective boron conjugate addition reaction, carried out using density functional theory (DFT) and artificial force induced reaction (AFIR) methods. The computed catalytic cycle for Cu(I)- and Cu(II)-based catalysts consists of three steps: (a) boron–boron bond cleavage of B2(pin)2, (b) boron conjugate addition on the β carbon of chalcone, and (c) protonation. The enantioselectivity of the reaction with LCuI or LCuII catalysts is solely governed at the boron conjugate addition step. The multicomponent (MC)-AFIR search and the subsequent DFT calculations for the LCuI catalyst determined transition states (TSs), which lead to CuI-O-enolate and CuI-C-enolate, and both equally contribute to the C–B bond formation with no enantioselectivity. On the other hand, a MC-AFIR search and the subsequent DFT calculations for the analogous LCuII catalyst showed that only the transition state (TS) leading to CuII-O-enolate con...