Visible‐Light‐Induced Diastereoselective Cascade Cyclization to Construct Polycyclic Spiroindolines

We herein reported, a visible‐light‐induced K2S2O8 mediated cascade reaction of 3‐(2‐isocyanoethyl)indoles with α‐oxocarboxylic acids leading to diastereoselective synthesis of polycyclic spiroindolines bearing an N‐formyl unit derivative utilising the alkali metal salt K2S2O8 as a mediator under mild reaction conditions. This study offers an illustration of α‐oxocarboxylic acids and 3‐(2‐isocyanoethyl)indoles‐based reactions as it shows the involvement of glyoxolate ions without decarboxylation to access polycyclic spiroindolines bearing an N‐formyl unit analogue. The batch process can be extended to a continuous flow system using a glass tube loaded with K2S2O8 placed between the PFA capillary reactor, which can greatly advance the reaction efficiency and can even be promoted to gram‐scale synthesis.