Copper(I)-Catalyzed Syntheses of Benzo[]fluorenes by the Cascade Reactions of 2-Alkynylbenzaldehyde -Tosylhydrazones and Aromatic Terminal Alkynes.

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