Controlled synthesis of substituted benzobasketene derivatives

The addition of benzyne to trans-7,8-dibromobicyclo[4.2.0]octa-2,4-diene (6) led to the formation of dibromide 7. The dehydrobromination of 7 followed by replacement of the Br-atom with a CN substituent gave 9. Photolysis of 9 in acetone at 254 nm yielded the desired monosubstituted benzobasketene derivative 10. Bromination of monobromide 8 followed by dehydrobromination furnished the symmetrically substituted dibromo compound 15. Further bromination of 7 followed by dehydrobromination resulted in the formation of the dibromides 20 and 21. Substitution of the Br-atoms in 15, 20, and 21 with CN substituents and photolysis of the formed dicarbonitriles 16, 23, and 24 gave the target benzobasketene-dicarbonitriles 17, 25, and 26, respectively.