GaCl₃-catalyzed ortho-ethynylation of phenols

Phenols are ethynylated at the ortho position with silylated chloroethyne in the presence of a catalytic amount of GaCl₃ and lithium phenoxide. The lithium salt is essential for the catalysis, and addition of 2,6-di(tert-butyl)-4-methylpyridine inhibits desilylation and hydration of the products. The reaction can be applied to various substituted phenols giving the ortho-ethynylated products in high yields, and the turnover numbers based on GaCl₃ are between 8 and 10. The reaction mechanism involves addition of in situ formed phenoxygallium to the haloethyne followed by the elimination of GaCl₃.