Chiral spirooxindoles are privileged heterocyclic motifs, which are widely found in natural alkaloids and pharmaceuticals. Moreover, the construction of chiral spiro-cyclic frameworks is a long-lasting challenge in organic synthesis. The past four years have witnessed significant developments in this field, and this feature article outlines the recent progress in the catalytic asymmetric synthesis of spirooxindoles, including the contributions of our group. The catalytic asymmetric construction of spirooxindoles has greatly benefited from the utilization of oxindole derivatives as starting materials, including isatin derivatives, methyleneindolinones, indolin-2-one derivatives and isatin-derived 3-indolylmethanols. This article is divided into sections according to the size and type of the generated spiro-ring fused at the C3-position of the oxindole core (from three-membered to seven-membered spiro-rings), and representative examples are given with illustrations. In addition, the enantioselective construction of bispirooxindole frameworks is also discussed in the last section.
The first enantioselective construction of a new class of axially chiral naphthyl-indole skeletons has been established by organocatalytic asymmetric coupling reactions of 2-naphthols with 2-indolylmethanols (up to 99 % yield, 97:3 e.r.). This approach not only affords a new type of axially chiral heterobiaryl backbone, but also provides a new catalytic enantioselective strategy for constructing axially chiral biaryl scaffolds by making use of the C3-electrophilicity of 2-indolylmethanols.
The first catalytic asymmetric construction of 3,3′‐bisindole skeletons bearing both axial and central chirality has been established by organocatalytic asymmetric addition reactions of 2‐substituted 3,3′‐bisindoles with 3‐indolylmethanols (up to 98 % yield, all >95:5 d.r., >99 % ee). This reaction also represents the first highly enantioselective construction of axially chiral 3,3′‐bisindole skeletons, and utilizes the strategy of introducing a bulky group to the ortho‐position of prochiral 3,3′‐bisindoles. This reaction not only provides a good example for simultaneously controlling axial and central chirality in one operation, but also serves as a new strategy for catalytic enantioselective construction of axially chiral 3,3′‐bisindole backbones from prochiral substrates.
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