Manganese-catalysed C2 allylation and deuteration of indoles in water

Mn-catalysed C–H activation has emerged as a useful sustainable methodology for the formation of new C–C bonds. To date most of the protocols are described in organic solvents. Water as solvent, on the other hand, would be highly advantageous, but is often incompatible with organometallic chemistry. Herein, we describe the C–H activation of indoles using an unmodified, commercially available manganese catalyst in water. Two types of valuable allyl groups can be added and a good substrate scope is described. Substitution at the C-3 group is tolerated, allowing access to medicinally important frameworks, and the reaction works on a gram scale. Finally, harnessing the tolerance of water as the reaction medium, D₂O can be used as an inexpensive source of deuterium for the C-2 labelling of indoles.