C1-Symmetric 1,2-Diaminobicyclo[2.2.2]octane Ligands in Copper-Catalyzed Asymmetric Henry Reaction: Catalyst Development and DFT Studies

Abstract

Chiral tetra- and bidentate ligands derived from the (R)-1,2-diaminobicyclo[2.2.2]octane scaffold were synthesized, and the influence of the N,N′-substituents of the ligand on the catalytic activity of their corresponding copper(II) complexes toward the nitroaldol reaction was investigated. Among them, the complex generated in situ by the interaction of the (R)-N,N′-bis(1-naphthylmethyl)-1,2-diaminobicyclo[2.2.2]octane ligand with Cu(OAc)2 proved to be the most effective for the asymmetric Henry reaction of nitromethane with various aldehydes to provide β-nitro alcohols in moderate to good yields and good enantioselectivity (up to 86 %). In an attempt to rationalize the factors that control enantiodifferentiation, the most stable geometries of this C1-symmetric bicyclic copper ligand complex and the plausible transition structures of the nitroaldol reaction were investigated by DFT calculations.