GaCl(3)-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.
Department of Organic Chemistry, Graduate School of Pharmaceutical Sciences, Tohoku University, Aoba, Sendai 980-8578, Japan.
Katsumi
K
Kobayashi
Mieko
M
Arisawa
Masahiko
M
Yamaguchi