COUPLING REACTIONS OF ORTHO-SUBSTITUTED ARYL HALIDES WITH ALKYNES - THE SYNTHESIS OF FUNCTIONALIZED 1-NAPHTHYLACETYLENES, 1-(1-NAPHTHYL)-2-PHENYLACETYLENES, AND 1,2-BIS(1-NAPHTHYL)ACETYLENES

Coupling of 2-functionalized 1-naphthyl halides with gaseous acetylene , (trialkylsilyl)acetylenes, and aryl acetylenes under Pd(PPh3)(4) or Pd(PPh3)(4)/CuI catalysis has been investigated to prepare 1-naphthyl- , 1-(1-naphthyl)-2-phenyl-, and 1,2-bis(1-naphthyl)acetylenes with var ious ortho substituents, i.e., the -CH3, -CH2OH, -CO2Me, and -CH2OCH2C =CCH3 groups. The reaction conditions have been optimized (yields up r o 96 %) by changing halogen atom in aryl halides, solvent, alkyl in (t rialkylsilyl)acetylenes, and catalyst (Pd(0) vs. Pd(0)/Cu(I)). In case of 1-naphthyl iodide with a tethered alkyne unit, coupling has been o bserved to compete with a cascade of intramolecular Heck-type reaction s. The mechanism of beta-elimination of a hydridopalladium species has been discussed. 1-Naphthyl bromide bearing the -CO2Me group has been found to be susceptible to nucleophilic aromatic substitution with a s olvent. The successful synthesis of an unsymmetrical 1-(1-naphthyl)-2- phenylacetylene derivative has been shown to depend critically on comb ination of aryl halide/aryl acetylene. (C) 1998 Elsevier Science Ltd. All rights reserved.