F-Tag Induced Acyl Shift in the Photochemical Cyclization of o-Alkynylated N-Alkyl-N-acylamides to Indoles

A photochemical cyclization of F-tagged, o-alkynylated N-alkylamides to indoles catalyzed by [Ir(dF(CF3)ppy)(2)(dtbpy)]PF6 is presented. This straightforward and efficient reaction involves an intramolecular rearrangement due to the presence of an electron withdrawing group in the acyl moiety and is the first example of photochemically induced 1,3-acyl shift in the cyclization towards 3-acylindoles. A four-step reaction sequence including the photoreaction as a key step to the desired indoles has been developed and optimized. The compatibility of differently substituted F-tagged precursors with the photocyclization step was investigated and the robustness of this step towards modifications could be shown. In total, 16 so far unknown derivatives with diverse modifications in positions N1 and C2, bearing a pentadecafluorooctanoyl moiety as F-tag, were synthesized in very good yields and fully characterized.