Heterogeneous Palladium Catalysts Applied to the Synthesis of 2- and 2,3-Functionalised Indoles

Heterogeneous palladium catalysts ((Pd(NH3)4) 2 þ /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 stand- ard reaction conditions (polar solvent, 808C). 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 ex- pected compound with ¼ 35% yield after 12 days of reaction, which is comparable to the homogeneous catalyst, Pd(OAc)2 ( ¼ 48% yield). In the course of the study, the dual reactivity of the indole nucleus was demonstrated: aryl bromides gave clean CC coupling while aryl iodides led to a clean CN cou- pling.

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