Carbon-carbon bond formation reaction of zirconacyclopentadienes with alkynes in the presence of Ni(II)-complexes

Zirconacyclopentadienes, prepared from two alkynes or a diyne, reacted with the alkyl-, trimethylsilyl-, or alkoxy-substituted third alkyne as well as an alkyne with an electron-withdrawing group in the presence of a stoichio metric amount of NiBr2(PPh3)(2) to give benzene derivatives in good yields. Heteroatom-containing a diynes such as dipropargylbenzylamine and propargy l-homopropargylbenzylamine gave ispindoline and tetrahydroisoquinoline deri vatives in good to high yields. This procedure was also used for the select ive preparation of benzene derivatives from three different alkynes. The us e of trimethylsilyl-substituted alkyne as the first, second or third alkyne afforded desilylated benzene derivatives. The reaction of zirconacyclopent adienes with allenes gave benzene derivatives as a mixture of two isomers.