Coupling reactions of ortho-substituted halobenzenes with alkynes. The synthesis of phenylacetylenes and symmetrical or unsymmetrical 1,2-diphenylacetylenes

The Pd- or Pd/Cu-catalyzed coupling reactions of halobenzenes bearing the m ethyl, hydroxymethyl, acetoxymethyl, methoxycarbonyl, or both methoxy and 4 ,4-dimethyl-4,5-dihydro-1,3-oxazol-2-yl groups in the ortho-position with g aseous or metallated acetylene, (trialkylsilyl)acetylenes, and arylacetylen es have been systematically studied. Various functionalized aryl- or diaryl acetylenes have been synthesized in good to excellent yields. Whereas addit ional fluoro, nitro, or methoxy group attached to the benzene ring does not interfere in the coupling reactions, the presence of a methoxycarbonyl req uires a careful optimization of reaction conditions to achieve moderate yie lds.