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

We herein reported, a visible‐light‐induced K 2 S 2 O 8 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 K 2 S 2 O 8 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 K 2 S 2 O 8 placed between the PFA capillary reactor, which can greatly advance the reaction efficiency and can even be promoted to gram‐scale synthesis.