The dichotomy between benzene and fulvene formation in palladium-catalyzeddomino tricyclizations of 2-bromotetradec-1-ene-7,13-diynes

2-Bromotetradec-l-ene-7,13-diynes 1, 5, 12 with different substituents at t he acetylenic terminus under palladium catalysis have been found to either yield an angularly bisannelated benzene derivative 3 (79%), or fulvene deri vatives of type 5 (52-74%) as well as monoannelated fulvenes 13b-e (32-48%) . The mechanisms for all three reaction modes most probably involve intramo lecular 5-exo-trig carbopalladations of an intermediate 1,3,5-hexatrienyl-6 -palladium bromide intermediate.