An unexpected reaction of indole derivatives and EAA catalyzed with InCl3

When indole derivatives reacted with ethyl acetoacetate (EAA) using Indium(III) chloride (InCl3) as a catalyst, cyclobutenes were obtained unexpectedly. The structure was identified by 2D-NMR and HRMS. Thus our data maybe established a new method to synthesize cyclobutenes, at least for the indole based cyclobutenes. A plausible mechanism for this surprising reaction was also proposed.