Au(PPh3)Cl/AgOTf/TsOH-Catalyzed Cascade Reaction between 1-(2-Hydroxyphenyl)-propargyl Alcohols and β-Oxoketones (Amides, Acid): Diastereoselective Construction of cis-3a,8a-Dihydrofuro[2,3-b]benzofuran Framework

In the Au(PPh3)Cl/AgOTf/TsOH/MeCN/N2/25 °C system, diastereoselective synthesis of cis-3a,8a-dihydrofuro[2,3-b]benzofuran derivatives with a substituent at the 8a-position has been achieved by using 1-(2-hydroxyphenyl)-3-arylprop-2-yn-1-ols and β-oxoketones (amides, acid) as starting materials. The studies revealed that the acidity of methylene in substrates plays a key role in the differential reactions. A stronger acidity of the methylene is favorable in the desired conversion. The unique role of TsOH as an additive acid in the synthesis strategy has been rationalized. 2-Oxo-phosphonate, 2-oxo-sulfonate, and 3-oxobutanoate are suitable for the conversion.