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 SO2Ph, 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 ZrCp2Cl2, ZrCp2MeCl, or ZrCp2Me2 in conjunction with the use of a deficient amount (0.9 molar equiv.) of I-2 for subsequent iodinolysis. (C) 2007 Elsevier B.V. All rights reserved.