Palladium‐Catalyzed Synthesis of 2‐Aminoindoles by a Heteroanulation Reaction

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

“…The N-tosyl-2-idodoaniline was prepared according a procedure reported in the literature. [30] Characterisation All solid-state NMR spectra were recorded on a Bruker DSX-300 or Avance-500 spectrometer equipped with a standard 4 mm probehead. The spinning rate was typically 10 kHz.…”

“…Recently, a new disconnection pathway based on the intramolecular cyclisation of N-alkynyl-2-haloanilides followed by a C À N coupling reaction with primary or secondary amines has been reported by Witulski et al (route 3, disconnection a & d). [30] Another commonly used procedure for the synthesis of 2-functionalised indole rings was from 2-iodoaniline and alkynes. [31 -33] This procedure usually requires two steps: the introduction of the ethynyl group onto the benzene ring, usually known as a Sonogashira C À C coupling reaction, followed by a heteroannulation, both of which are efficiently catalysed by Pd species.…”

Palladium on activated carbon: a valuable heterogeneous catalyst for one-pot multi-step synthesis

“…This indicates that the heteroannulation is rapid under reaction conditions. In the absence of CuI the reaction proceeds but very slowly, leading to a GC yield of 2-phenylindole 8 of 25% after 24 h. This indicates the relevance of the co-catalysts played by copper species in the Sonogashira coupling reaction or the heteroannulation [26][27][28].…”

Recent Developments in Palladium-Catalyzed Heterocycle Synthesis and Functionalization

“…For example, Cossy has recently reported a tandem Heck cyclization/cross-coupling reaction of ynamides and boronic acids that affords 3-(arylmethylene)isoindolinones (eq 9) [18]. The Pd-catalyzed reaction of a related N-ethynyl aniline substrate 3 with a primary or secondary amine affords a 2-aminoindole product (eq 10) [19]. In contrast to the transformation described above, this reaction is believed to proceed through initial oxidative addition of the aryl iodide to Pd(0) followed by alkyne complexation to afford 4.…”