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

Abstract

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 2Ph, 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) 2Cl 2 or, more conveniently, the stoichiometric amount of ZrCp 2Cl 2, ZrCp 2MeCl, or ZrCp 2Me 2 in conjunction with the use of a deficient amount (0.9 molar equiv.) of I 2 for subsequent iodinolysis.