Isatins As Privileged Molecules in Design and Synthesis of Spiro-Fused Cyclic Frameworks

The unique potential of isatins to be used both as an electrophile and nucleophile and their easy availability have made them valuable building blocks in organic synthesis. The architecture of a spiro-cyclic framework has always been a challenging endeavor for synthetic organic chemists because it often requires synthetic design based on specific strategies. Due to steric strain, the presence of a spiro carbon atom induces easy rearrangements that can lead to different cyclic compounds. Recent years have witnessed emergence of asymmetric synthetic methods employing chiral auxiliaries or chiral catalysts with good stereocontrol furnishing products containing spirofused rings with superb enantioselectivity. In many cases, simple chemical transformations of the initially formed spirooxindoles have been performed to achieve spiro-oxindoles with different functionality.