m-Iodophenol (4a) was found to couple with 2-methylbut-3-yn-2-ol (5) in the presence of PdCl2–CuI–Ph3P-in triethylamine to afford 3-(3-hydroxy-3-methylbut-1-ynyl)phenol (6a), which was conveniently converted into m-ethynylphenol (7a). Under the same conditions, p-iodophenol did not couple with 5. However, p-iodo-1-[(tetrahydro-2H-pyran-2-yl)oxy]benzene (4b) did react with 5 to afford 1-[(tetrahydro-2H-pyran-2-yl)oxy]-4-[2-hydroxy-2-methyl-4-but-3-ynyl]benzene (6b), which was similarly converted into 1-[(tetrahydro-2H-pyran-2-yl)oxy]-4-ethynylbenzene (7b) with loss of acetone. Removal of the tetrahydropyranyl protecting group from 7b furnished p-ethynylphenol (8).
