Regio- and Stereoselective, Intramolecular [2+2] Cycloaddition of Allenes, Promoted by Visible Light Photocatalysis

Enallenylamides have been utilized for the synthesis of heterobicycle[4.2.0]octane derivatives via Ir/h & nu; promoted [2+2] cycloaddition reaction. The reaction specifically targets the distal double bond of the allene moiety, and results in the exclusive formation of the trans product. The process is conducted at room temperature and under an inert atmosphere. An extensive study on the substituent propensities during the cycloaddition step revealed variable effects. Electron-withdrawing groups conjugated with the double bond participating in the cycloaddition either hindered the process or reduced its yield. Conversely, electron-donating substituents enhanced the efficiency, resulting in product yields ranging from 60% to 88%. Our study also demonstrated the influence of protecting groups on the reaction pathway.