Remarkable electron-withdrawing effect of the Ph2P(O)-ethynyl group: Ph2P(O)-ethynyl-substituted aryl halides and copper acetylides for tailor-made Sonogashira couplings

Abstract

The electronic effect of the Ph₂P(O)-ethynyl group in Sonogashira couplings was investigated. Ph₂P(O)-ethynylphenyl iodide showed higher reactivity than diiodobenzene because of the electron-withdrawing effect of the Ph₂P(O) group. Copper acetylide, which was prepared in situ from Ph₂P(O)-ethyne, exhibited poor nucleophilicity and reacted with aryl iodides in Sonogashira couplings, but did not react with aryl bromides. This high selectivity enabled practical syntheses of a cyclic phenyleneethynylene and unsymmetrically substituted 9,10-bis(ethynyl)anthracenes.