Halocyclization of 2-alkynylthioanisoles by cupric halides: synthesis of 2-substituted 3-halobenzo[b]thiophenes

Reaction of 2-alkynylthioanisoles 3 with 2 equiv of CuX2 (X=Br or Cl) in refluxing CH3CN for 2.5 h gave the 2-substituted 3-halobenzo[b]thiophenes 4 in good yields.