Unusually high ortho-selectivity in electrophilic aromatic substitution promoted by GaCl3

1,4-Bis(trimethylsilyl)buta-1,3-diyne in the presence of GaCl3 reacts with aromatic hydrocarbons at -90 to -100 degrees C yielding 2-arylbut-1-en-3-ynes; the reactions exhibit an unusually high tendency to alkenylate the o-position of alkyl substituents; toluene, ethylbenzene and isopropylbenzene react predominantly to exclusively at the o-position while o-xylene and 1,2,3,4-tetrahydronaphthalene react at the 3 and 5-position, respectively.