Synthesis of enantiomerically pure bicycle[4.2.0]octanes by Cu-catalyzed [2+2] photocycloaddition and enantiotopos-differentiating ring opening

(Chemical Equation Presented) 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.