Bicyclo[2.1.1]hexanes by Visible Light-Driven Intramolecular Crossed [2 + 2] Photocycloadditions

Bicyclo[2.1.1]hexanes
have become increasingly popular building
blocks in medicinal chemistry as bridged scaffolds that provide unexplored
chemical space. We herein report a visible light-driven approach to
these compounds that relies on an intramolecular crossed [2 + 2] photocycloaddition
of styrene derivatives enabled by triplet energy transfer. Bicyclo[2.1.1]hexanes
were obtained in good to high yields (19 examples, 61%-quantitative
yield) and allowed for further functionalizations by consecutive reactions,
thereby opening different pathways to decorate the aliphatic core
structure.