Isocyanide‐Based Multicomponent Reactions: Concise Synthesis of Spirocyclic Oxindoles with Molecular Complexity by Using a [1,5]‐Hydrogen Shift as the Key Step

A concise multicomponent reaction of isocyanide, α‐substituted allenoate, and methyleneindolinone has been disclosed. This protocol provides a fast and straightforward approach to synthesize unusual tricyclic oxindoles in an efficient and atom‐economic manner. Mechanistically, the present cycloaddition may proceed through a cascade sequence involving double Michael addition, double cyclization, double [1,5]‐hydrogen shift, and group migration. The introduction of a special alkyl group to the allenoate is believed to play a key role in the cascade reaction. This method also features a broad substrate scope, which is particularly useful for the delivery of a large number of compounds.