A novel solvent-controlled chemoselective palladium-catalyzed oligomerization of tert-butyl acetylene was reported in this paper. The reaction was carried out in benzene/n-BuOH binary solvent system smoothly. When benzene was preponderating component in the binary solvent system, a cyclotrimerization process occurred to give 1,3,5-tri-tert-butylbenzene via a mechanism of three acetylene molecular stepwise insertions forming σ-butadienyl-Pd and σ-hexatrienyl-Pd intermediates. While when the polar, protic and strong coordinating solvent, n-BuOH, which could help to cleave the C—Pd σ-bonds and solvate Pd(II) cation, Cu(II) cation, halo anion and σ-butadienyl-Pd inter-mediate etc., was increased to a certain ratio in the binary solvent system, the reaction proceed readily via n-BuOH promoted mechanism to give (3Z,5Z)-2,2,7,7-tetramethyl-3,6-dichloro-3,5-octadiene or (3Z,5Z)-2,2,7,7-tetramethyl-3,6-dibromo-3,5- octadiene, respectively, instead of cyclotrimerization product. Possible weak hydrogen bonds and n-π weak force between n-BuOH and tert-butyl acetylene (or σ-butadienyl-Pd intermediate) were also in favor of the n-BuOH promoted pathway. Mean-while, a coupling product 2,2,7,7-tetramethyl-3,5-octadiyne was given exclusively when the reaction was conducted in singular polar H₂O. Influences of the solvent, catalysts, and possible mechanism were discussed.

Key words: tert-butyl acetylene, palladium, oligomerization, chemoselectivity, solvent