Au(PPh<sub>3</sub>)Cl/AgOTf/TsOH-Catalyzed\nCascade\nReaction between 1‑(2-Hydroxyphenyl)-propargyl Alcohols and\nβ‑Oxoketones (Amides, Acid): Diastereoselective Construction\nof <i>cis</i>-3a,8a-Dihydrofuro[2,3‑<i>b<

In\nthe Au(PPh<sub>3</sub>)Cl/AgOTf/TsOH/MeCN/N<sub>2</sub>/25 °C\nsystem, diastereoselective synthesis of <i>cis</i>-3a,8a-dihydrofuro[2,3-<i>b</i>]benzofuran derivatives with a substituent at the 8a-position\nhas been achieved by using 1-(2-hydroxyphenyl)-3-arylprop-2-yn-1-ols\nand β-oxoketones (amides, acid) as starting materials. The studies\nrevealed that the acidity of methylene in substrates plays a key role\nin the differential reactions. A stronger acidity of the methylene\nis favorable in the desired conversion. The unique role of TsOH as\nan additive acid in the synthesis strategy has been rationalized.\n2-Oxo-phosphonate, 2-oxo-sulfonate, and 3-oxobutanoate are suitable\nfor the conversion.