Solvent-controlled chemoselective palladium-catalyzed oligomerization of tert-butyl acetylene

A solvent-controlled chemoselective palladium-catalyzed oligomerization of tert-butyl acetylene was reported in this paper. The reaction was carried out smoothly in benzene/n-BuOH binary solvents system. When benzene, unpolar aprotic solvent, became preponderating in the binary solvents system, a cyclotrimerization process occurred to produce 1,3,5-tri-tert-butylbenzene via a mechanism of three acetylene molecular to insert step by step forming σ-butadienyl-Pd and σ-hexatrienyl-Pd intermediates, etc., while when the polar protic component n-BuOH, which dissolves more CuX2 than benzene in the process, was increased to a certain extent in the binary solvents system, the reaction proceed readily 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. Meanwhile, 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 solvents, catalysts, as well as possible mechanisms in the reaction were discussed in this paper.

Recently, we found that solvent play an important role in influencing the chemoselectivity of the Pd(II)-catalyzed reactions. Solvent controls the chemoselectivity of PdX2-catalyzed oligomerization of tert-butyl acetylene: 1,3,5-tri-tert-butylbenzene, (3Z, 5Z)-2,2,7,7-tetramethyl-3,6-dichloro-3,5-octadiene, (3Z, 5Z)-2,2,7,7-tetramethyl-3,6-dibromo-3,5-octadiene and 2,2,7,7-tetramethyl-3,5-octadiyne were obtained, respectively, by regulating the solvent. Figure optionsDownload as PowerPoint slide