Water-Promoted Indole Migration of Bis(indol-3-yl)-ynamides Using Zn(OTf)₂ as a Lewis Acid Catalyst

A zinc(II)-catalyzed cycloisomerization of bis(indol-3-yl)-ynamides in the presence of water has been established for constructing carbonyl-containing bisindole derivatives in moderate to good yields with good functional group tolerance and a broad substrate scope. The reaction proceeds through a 7<i>-endo-dig</i> cyclization followed by a <i>pseudo</i>-1,6-indole-migration, which is supported by isotope ¹⁸O-labeling experiments. Moreover, large-scale synthesis and further synthetic transformation of the obtained product have been also presented.