Achiral Counteranion-Induced Reversal of Enantioselectivity in Ni(II)-Catalyzed Friedel-Crafts Alkylation/Annulation of 2-Naphthols.

An achiral counteranion-induced reversal of enantioselectivity in Ni(II)-catalyzed Friedel-Crafts alkylation/annulation of 2-naphthols with β,γ-unsaturated α-keto esters was achieved. Using imidazolidine pyrroloimidazolone pyridine as the ligand and Ni(acac) 2 as the Lewis acid, diverse naphthopyran derivatives were obtained in good yields (up to 94% yield) and high enantioselectivities (up to 99% ee). In the presence of Ni(OTf) 2 as the Lewis acid, a series of chiral naphthopyran derivatives were obtained in good yields and with a controlled switch in stereoselectivity. DFT calculations reveal that the achiral counteranions regulate H-bonding interactions between counteranions with the N-H of the ligand and the O-H of 2-naphthol.