Regioselective Direct C‐Alkenylation of Indoles

Abstract

The direct introduction of alkenyl groups into the indole framework avoiding its preliminary functionalization can be carried out using different synthetic strategies. Transition-metal complexes facilitate the C-H activation of indoles or alkenes allowing an efficient Csp - Csp bond formation. The hydroindolation of alkynes catalyzed by the same metal complexes or various acidic promoters can also be pursued for the alkenylation process. Conjugate addition of electron-poor alkenes and direct condensation of carbonyl derivatives with indoles are also of interest for this purpose. The regiochemical control can be exploited using the intrinsic C-3 reactivity of the indole ring. The introduction of a suitable directing group at the nitrogen atom allows the preparation of C-2 alkenylated derivatives by transition metal catalyzed reactions. This review collects the fundamental contributions in this field reported in literature during the last fifteen years.

Pd-Catalyzed Intermolecular Dehydrogenative Heck Reactions of Five-Membered Heteroarenes

“…The topic continued to retain the attention of researchers resulting into papers with different N-protecting groups and experimental conditions. Reviews not limited to palladium catalysis and DHR have been published [77][78][79]. As pointed in the introduction chapter, we will limit the examples to the DHRs of the heterocycle (For reactions at C4, C5, C6, and C7 positions of the benzenoid ring, see [18]).…”

One‐Pot Synthesis of 3‐(2‐Fluoroalkenyl)indoles

“…Although many different methods of synthesis of 3‐vinylindoles have been extensively investigated and described, however, to the best our knowledge none of 3‐(2‐fluoro‐1‐arylvinyl)‐1H‐indoles have been mentioned in literature yet. Apparently this is related to elusive unstable nature of fluoroacetylenes that could be precursors for synthesis of the such structures by hydroarylation of alkynes with indoles; a commonly used method for preparation of 3‐alkenylindoles (Scheme ).…”

“…Apparently this is related to elusive unstable nature of fluoroacetylenes that could be precursors for synthesis of the such structures by hydroarylation of alkynes with indoles; a commonly used method for preparation of 3‐alkenylindoles (Scheme ). [19a], In this context, formal result of the sequence herein proposed looks like the potential reaction of indoles with fluoroacetylenes.…”

Rhenium‐ and Manganese‐Catalyzed Selective Alkenylation of Indoles

“…Thus, numerous methods have been developed for the regioselective synthesis of C2 and C3 functionalized indoles . Compared to the well established indole C2‐arylation, direct regioselective C2‐alkenylation is less explored ,. In general, alkenes are used as reaction partners for the alkenylation of indoles .…”