Heterogeneous palladium catalysts applied to the synthesis of 2- and 2,3-functionalised indoles

Heterogeneous palladium catalysts ([Pd(NH3)(4)](2+)/NaY and [Pd]/SBA-15) were applied to the synthesis of 2-functionalised indoles, giving generally high conversions and selectivities (> 89% yield) using only 1 mol % [Pd]-catalyst under standard reaction conditions (polar solvent, 80 degrees C). For the synthesis of 2,3-functionalised indoles by cross-coupling arylation, the [Pd]/SBA-15 catalyst was found to be particularly interesting, producing the expected compound with =35% yield after 12 days of reaction, which is comparable to the homogeneous catalyst, Pd(OAc)(2) (=48% yield). In the course of the study, the dual reactivity of the indole nucleus was demonstrated: aryl bromides gave clean C-C coupling while aryl iodides led to a clean C-N coupling.