Water, an Essential Element for a ZnII‐Catalyzed Asymmetric Quinone Diels‐Alder Reaction: Multi‐Selective Construction of Highly Functionalized cis‐Decalins

A ZnII complex of a C2‐chiral bisamidine‐type sp2N bidentate ligand (LR) possessing two dioxolane rings at both ends catalyzes a highly efficient quinone asymmetric Diels‐Alder reaction (qADA) between o‐alkoxy‐p‐benzoquinones and 1‐alkoxy‐1,3‐butadienes to construct highly functionalized chiral cis‐decalins, proceeding in up to a >99:1 enantiomer ratio with a high generality in the presence of H2O (H2O:ZnII=4–6:1). In the absence of water, little reaction occurs. The loading amount of the chiral ligand can be minimized to 0.02 mol % with a higher Zn/LR ratio. This first success is ascribed to a supramolecular 3D arrangement of substrates, in which two protons of an “H2O‐ZnII” reactive species make a linear hydrogen bond network with a dioxolane oxygen atom and one‐point‐binding diene; the ZnII atom captures the electron‐accepting two‐points‐binding quinone fixed on the other dioxolane oxygen atom via an n‐π* attractive interaction. The mechanisms has been supported by 1H NMR study, kinetics, X‐ray crystallographic analyses of the related ZnLR complexes, and ligand and substrate structure‐reactivity‐selectivity relationship. Testing the waters: A new [Zn(H2O)LR]2+ complex has been developed to realize a highly efficient asymmetric quinone‐Diels‐Alder reaction. The presence of the two oxygen atoms of LR at the reaction site with a spatially accessible environment and “H2O” in the reaction system are essential. o‐Alkoxy‐p‐benzoquinone and 1‐alkoxy‐1,3‐butadiene are fixed by a linear hydrogen bond network and n‐π* attractive interaction to realize the high reactivity and multi‐selectivity.