Palladium-Catalyzed Sonogashira Coupling and Iodocyclization Route to 3-Iodofurans

Significance

Reported is a two-step procedure for the synthesis of 2,5-disubstituted 3-iodo­furans. Thus, Z-β-bromoenol acetates are treated with terminal acetylenes in a Sonogashira coupling to afford conjugated enyne acetates which, when subjected to reaction with iodine, undergo halocyclization to afford 2,5-disubstituted 3-iodo­furans in good to excellent yields. Six substrates failed to undergo reaction in the second step, i.e., when R^² = H₂NC₆H₄, Fc, cyclohexen-1-yl, C(OH)Me₂, TMS and c-Pr. The claim that the nature of the R^¹ group has very little impact on the reaction is not fully substantiated by the cases examined. Otherwise, the substrate scope was very well studied in terms of R^² and, judging by the attained yields, the reaction either works well or not at all. Furthermore, some of the 3-iodofuran products were shown to undergo Sonogashira coupling with terminal alkynes to give 3-alkynyl furans in good yields.