Metal-free [2+2]-photocycloaddition of unactivated alkenes enabled by continuous flow processing

We report a continuous flow approach generating bicyclic cyclobutanes from unactivated alkenes in a metal-free manner that is inspired by the Kochi-Salomon reaction. A filtered Hg-lamp in combination with a simple flow set-up and acetone as UV light-absorbing co-solvent are crucial for this method thus showcasing attractive features for further exploitations.