Hydrogen Bonding and Alcohol Effects in Asymmetric Hypervalent Iodine Catalysis: Enantioselective Oxidative Dearomatization of Phenols

摘要

The enantioselective oxidative dearomatization of phenols and their analogues is a key reaction for the synthesis of several natural products. Conventionally, enantioselective transition-metal catalysis has been used for these trans-formations. Recently, some research groups have reported catalytic enantioselective oxidative dearomatization reactions using chiral hypervalent iodine compounds. However, the catalytic activities and enantioselectivities are moderate, and the substrate scope of the oxidation reactions is limited to 1-naphthol derivatives. Herein, we describe the rationally designed chiral iodoarene 1, which is derived from chiral 2-aminoalcohol, as a chiral precatalyst for the first enantioselective catalytic oxidative dearomatization of phenol derivatives 3 to give the desired cyclohexadienone spirolactones 4 and the subsequent Diels-Alder adducts 5 with high to excellent enantioselectivities (87-99% ee, Scheme 1). Active iodine(III) species 2 would be generated in situ from C2-symmetric and conformationally flexible chiral iodoarene 1 and meta-chloroperoxybenzoic acid (m-CPBA). We envisioned that a suitable chiral environment might be constructed around the iodine(III) center via intramolecular hydrogen bonding interactions between the acidic amido protons and the iodine(III) ligands (L).