A series of isoprene coupling dimers bonded at 1-2, 1-3, 1-4, 2-4, 3-4, or 4-4 position was prepared by regiocontrolled catalysis of trasition metals or without catalysts in the reaction of 2-methyl-2-butene-1,4-diylmagnesium or 3-methyl-2-butenylmagnesium chloride with C5-alkenyl halides.