Direct C-glycosylation of indole with unprotected mono-, di-, and trisaccharides: a one-pot synthesis of 1-deoxy-1,1-bis(3-indolyl)alditols

1-Deoxy-1,1-bis(3-indolyl)alditols were synthesized by reacting 2.5 equiv of indole with 1 equiv of the following seven monosaccharides (d-galactose, d-mannose, d-allose, 2-deoxy-d-arabinohexose (2-deoxy-d-glucose), d-arabinose, l-arabinose, d-xylose), two disaccharides (d-lactose, d-maltose), and a trisaccharide (d-maltotriose) in 1:1 EtOH-H2O at room temperature, or at 40 or 50 °C, in the presence of 5 mol % scandium(III) trifluoromethanesulfonate [Sc(OTf)3], in a one-pot reaction, in 36-95% yields.