Benzo[b]fluorenes were synthesized via CuI-catalyzed cascade reactions of 2-alkynylbenzaldehyde N-tosylhydrazones and aromatic terminal alkynes in the presence of base including the formation of the benzoenyne-allene intermediate in situ and its Schmittel cyclization. Density functional theory calculation was performed to give the energy difference for the formation of 5-phenyl-11H-benzo[b]fluorene and 1,2-diphenyl-1H-cyclobuta[a]indene from the proposed diradical intermediates.