Gold(I)-Catalyzed Dearomative [2+2]-Cycloaddition of Indoles with Activated Allenes: A Combined Experimental–Computational Study

The gold-catalyzed synthesis of methylidene 2,3- cyclobutane-indoles is documented through a combined ex- perimental/computational investigation. Besides optimizing the racemic synthesis of the tricyclic indole compounds, the enantioselective variant is presented to its full extent. In par- ticular, the scope of the reaction encompasses both arylox- yallenes and allenamides as electrophilic partners providing high yields and excellent stereochemical controls in the desired cycloadducts. The computational (DFT) investigation has fully elucidated the reaction mechanism providing clear evidence for a two-step reaction. Two parallel reaction path- ways explain the regioisomeric products obtained under ki- netic and thermodynamic conditions. In both cases, the dearomative CC bond-forming event turned out to be the rate-determining step.