Synthesis of Enantiomerically Pure Bicyclo[4.2.0]octanes by Cu‐Catalyzed [2+2] Photocycloaddition and Enantiotopos‐Differentiating Ring Opening

Fooling Mother Nature: When the bicyclo[4.2.0]octanes A are bridged as in precursors B (Z=CO), the otherwise impossible [2+2] photocycloaddition reaction of 1,7-dienes is possible with substrates such as C. A subsequent Baeyer–Villiger oxidation serves to desymmetrize substrates B and establishes a general approach to enantiomerically pure products A.