Copper-Catalyzed Sulfenylation, Sulfonylation, and Selenylation of 2,3-Allenoic Acids with Disulfides or Diselenides.

The efficient copper-catalyzed sulfenylation and selenylation of 2,3-allenoic acids with disulfides or diselenides were developed, respectively. These reactions proceeded through tandem radical addition/intramolecular cyclization processes, affording a series of 4-sulfenylated and 4-selenylated butenolides in moderate to excellent yields. Moreover, 4-sulfonylated butenolides could also be obtained by sulfenylation of 2,3-allenoic acids and subsequent oxidation. Further transformation of the sulfur- and selenium-containing butenolides afforded the corresponding furan derivatives in good yields.