When indoles meet allene and its derivatives

The allene functional group and the indole ring have emerged as recurring building blocks in organic chemistry due to their diverse reactivity and straightforward preparation. In addition, the biological properties and natural occurrence of indole give a remarkable added-value to newly-prepared indole-based structures. In the last decade, the combination of allenes and indoles as co-reactants has revealed a fruitful reactivity allowing the synthesis of complex structures and the investigation of new mechanistic pathways, such as the challenging asymmetric nucleophilic addition using optically pure allenes as chirality transfer agents, the double nucleophilic addition through metal carbene intermediates, or novel hybrid catalysis in a bimetallic system. Herein we report a critical review into the wide and fascinating ways allenes and indoles can interact, and the structural diversity that can be therefore achieved.