Palladium-Catalyzed Cross-Coupling Reactions of 1,2-Diiodoalkenes with Terminal Alkynes: Selective Synthesis of Unsymmetrical Buta-l,3-diynes and 2-Ethynylbenzofurans

摘要

(E)- 1,2-Diiodoalkenes were found to be effective building blocks for the preparation of unsymmetrical buta-1,3-diynes and 2-ethynylbenzofurans. In the presence of palladium(II) acetate and copper(I) iodide, unsymmetrical buta-l,3-diynes were selectively obtained in moderate to good yields. Moreover, 2-ethynylbenzofurans were obtained in one pot from the reaction of 2-ethynylphe-nol with (E)-l,2-diiodoalkenes, palladium(II) acetate, andcopper(I) iodide by simple heating.Buta-l,3-diynes are an important structural motif frequently found in a wide range of natural products, bioac-tive molecules, and functional materials; they are also extremely valuable intermediates in organic synthesis.1 Accordingly, considerable efforts have been devoted to the development of efficient methods for their preparation.1"8 The Glaser coupling reaction represents one of the most reported transformations using a copper complex as the catalyst.2 However, this technique is often unsatisfactory for the synthesis of unsymmetrical buta-l,3-diynes.