Synthesis of Fused Thiophene-Isoxazoles from 2-Alkynyl-3-Nitro-Thiophenes

Significance

Reported is the gold- or silver-­catalyzed cyclization of 2-alkynyl-3-nitro-thio­phenes to make fused thiophene-isoxazole systems. The authors postulate that this could ­occur from a ­cyclization-ring fragmentation-­cyclization sequence, because the most likely source of the carbonyl oxygen atom is from the ­nitro group, as the reactions were performed ­under anhydrous conditions. More work examining the mechanism of this reaction and a more ­detailed test of the scope and limitations is promised and should prove interesting.