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

Abstract

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 CuX 2 than benzene in the process, was increased to a certain extent in the binary solvents system, the reaction proceed readily to give (3 Z, 5 Z)-2,2,7,7-tetramethyl-3,6-dichloro-3,5-octadiene or (3 Z, 5 Z)-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 H 2O. Influences of the solvents, catalysts, as well as possible mechanisms in the reaction were discussed in this paper.