Gold(I)-Catalyzed Dearomative [2+2]-Cycloaddition of Indoles with Activated Allenes: A Combined
Riccardo Ocello1, Assunta De Nisi1, Minqiang Jia2
1Department of Chemistry "G. Ciamician", Alma Mater Studiorum - University of Bologna, Via Selmi 2, 40126 Bologna (Italy).
Abstract:
The gold-catalyzed synthesis of methylidene 2,3-cyclobutane-indoles is documented through a combined experimental/computational investigation. Besides optimizing the racemic synthesis of the tricyclic indole compounds, the enantioselective variant is presented to its full extent. In particular, the scope of the reaction encompasses both aryloxyallenes 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 pathways explain the regioisomeric products obtained under kinetic and thermodynamic conditions. In both cases, the dearomative CC bond-forming event turned out to be the rate-determining step.
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