Formation of stereodefined multiply substituted all-cis octatetraenes, tricyclo[4.2.0.02,5]octa-3,7-dienes and pentalenes via CuCl- or FeCl3-mediated dimerization of 1-lithiobutadienes and 1,4-dilithiobutadienes

Dimerization of 1-lithiobutadienes and 1,4-dilithiobutadienes depended remarkably on the substituents and metal halide reagents. Stereodefined multiply-substituted linear all-cis octatetraenes were prepared in moderate yields via FeCl3-mediated dimerization of 1-lithiobutadienes, while CuCl induced the dimerization of alkyl-substituted 1,4-dilithio-1,3-dienes to form linear all-cis octatetraenes and tricyclo[4.2.0.02,5]octa-3,7-dienes. Interestingly, stereodefined pentalene derivatives were also obtained when 1,4-dilithio-1,3-dienes possessed both phenyl and alkyl substituents.