Zirconium-catalyzed methylalumination of heterosubstituted arylethynes. Factors affecting the regio-, stereo-, and chemoselectivities.

The Zr-catalyzed methylalumination of heterosubstituted arylethynes containing O, S, Cl, and Si can proceed in high yields (>70%) and in a highly regio- and stereoselective manner (≥98-99%), although SO(2)Ph, Br, and Cl in a benzylic position present serious chemoselectivity-related problems. The low regioselectivity of 60% initially observed with o-ethynylphenol (1a) has been elevated to ≥98% through the use of either a catalytic amount of Zr(ebi)Cl(2) or Zr(2-Me-Ind)(2)Cl(2) or, more conveniently, the stoichiometric amount of ZrCp(2)Cl(2), ZrCp(2)MeCl, or ZrCp(2)Me(2) in conjunction with the use of a deficient amount (0.9 molar equivalent) of I(2) for subsequent iodinolysis.