Synthesis of derivatized indoles by photocatalyzed reactions in batch- and microreactors

This work investigated a novel photochemical cyclization to form indole derivatives from o-alkynylated F-tagged aniline derivatives, and wide applicability to synthesize differently functionalized indole systems bearing various substituents in the positions N-1, C-2, C-3, C-5 and C-6 was shown. Additionally, this reaction was systematically studied in a kinetic study in an in-house assembled capillary photo-microreactor. Further derivatization of the final F-tagged 3-acylindoles by the cleavage of the perfluorinated chain yielded a library of novel indole-3-carboxylic acid and indole-3-carboxylic acid ester derivatives. A straightforward and efficient four-step methodology for the synthesis of desired indole derivatives with high yields for single steps and the whole sequence was developed. Variing the conditions of single steps showed that all three steps of the reaction route to the cyclization precursors can be performed using the same solvent and base, providing the possibility to conduct this sequence as a continuous-flow without the need for in-line solvent switch or base exchange and without compromises with respect to the selectivity and yields of single steps.