Preparation of arylzinc halides by silver promoted oxidative metalation

Organozinc halides are useful reagents for organic synthesis, as witnessed by their wide use as nucleophiles in the Negishi coupling, a powerful and versatile reaction for carbon-carbon bond formation. Direct insertion of zinc metal into organic halides provides the most practical and atom-economical way for preparing these organometallic reagents. Nevertheless, oxidative metalation often has limited application due to long reaction times required by many substrates. We found that a catalytic amount of silver acetate efficiently promotes direct insertion of zinc metal to aryl iodides, having different structure, in ethereal solvent. Also electron-rich substrates rapidly undergo oxidative metalation. Arylzinc iodides thus formed give Negishi coupling products under mild reaction conditions. In all cases, reaction times required to provide full conversion in the metalation step are between 2 and 15 hours even on electron-rich substrates, which are scarcely reactive under the most commonly used reaction conditions.