Coupling reactions of ortho-substituted aryl halides with alkynes. The synthesis of functionalized 1-naphthyl-, 1-(1-naphthyl)-2-phenyl-, and 1,2-bis(1-naphthyl)acetylenes

Abstract

Coupling of 2-functionalized 1-naphthyl halides with gaseous acetylene, (trialkylsilyl)acetylenes, and aryl acetylenes under Pd(PPh 3) 4 or Pd(PPh 3) 4 CuI catalysis has been investigated to prepare 1-naphthyl-, 1-(1-naphthyl)-2-phenyl-, and 1,2-bis(1-naphthyl)acetylenes with various ortho substituents, i.e., the -CH 3, -CH 2OH, -CO 2Me, and -CH 2OCH 2CCCH 3 groups. The reaction conditions have been optimized (yields up to 96 %) by changing halogen atom in aryl halides, solvent, alkyl in (trialkylsilyl)acetylenes, and catalyst (Pd(O) vs. Pd(O) Cu(I) ). In case of 1-naphthyl iodide with a tethered alkyne unit, coupling has been observed to compete with a cascade of intramolecular Heck-type reactions. The mechanism of β-elimination of a hydridopalladium species has been discussed. 1-Naphthyl bromide bearing the -CO 2Me group has been found to be susceptible to nucleophilic aromatic substitution with a solvent. The successful synthesis of an unsymmetrical 1-(1-naphthyl)-2-phenylacetylene derivative has been shown to depend critically on combination of aryl halide/aryl acetylene.