Hydroformylation of 2‐Alkynylanilines: Toward an Alternative Methodology for the Synthesis of 3‐Substituted Indoles

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A potentially viable route for the synthesis of 3‐substituted indoles is presented herein. The methodology is based on a regioselective Rh‐catalysed hydroformylation of prepared 2‐alkyn‐1‐ylanilines. The requisite 2‐alkynylaniline substrates were prepared in high yields (>85 %) using the Pd‐catalysed Sonogashira reaction. A catalyst complex that comprises RhI(CO)(PPh3)3 and 1,2‐bis(diphenylphosphino)ethane as the ligand allowed the quantitative conversions of the alkynyl substrates with selectivities >75 % for the desired 3‐substituted indoles.