Translated abstract:
This work describes the synthesis of enantiomerically pure bicyclo[4.2.0]octanes by the combination of a [2+2]-photocycloaddition reaction with an asymmetric fragmentation reaction. Substituted 2,5-divinylcyclopentanols have been synthesized as new substrates for Cu-catalyzed photocycloaddition reactions. The tricyclo[4.2.02,5]nonanes could be obtained in yields of 72-89% and were transformed to the bicyclo[4.2.0]octanes by cleavage of the C1-bridge. For example, enatioselective, enzymatic Baeyer-Villiger oxidations have been used for the desymmetrization, and enantioselectivities up to 98% ee have been obtained. Also, Haller-Bauer cleavage reaction, an asymmetric variation of the Schmidt reaction, and a Rh-catalyzed rearrangement reaction have been used for the fragmentation of tricyclo[4.2.02,5]nonanes.