Ruthenium-catalyzed heteroannulation of anilines with alkanolammonium chlorides leading to indoles

Reduction of nitroarenes followed by propanol group transfer from tris(3‐hydroxypropyl)‐ amine and cyclization leading to quinolines under heterogeneous PdC catalysis

“…This protocol has been used for the synthesis of unsymmetrical amines and N‐heterocycles and for the study of the metabolism of amines 2–5. During the course of our ongoing studies toward transition metal‐catalyzed carbon–carbon and carbon–nitrogen bond forming reactions, we also reported on ruthenium‐catalyzed alkanol and alkyl group transfer from alkanol‐ and alkylamines to N‐atom anilines (amine exchange reaction), which eventually led to indoles, quinolines and benzimidazoles 6–13. Furthermore, in connection with this report, it was disclosed that nitroarenes can be directly used for the synthesis of indoles and quinolines via a ruthenium‐catalyzed reductive alkyl and alkanol group transfer from alkyl‐ and alkanolamines since nitroarenes are precursors of anilines from the viewpoint of industrial organic chemistry 14–21.…”

Recent Progress of New Catalytic Synthetic Methods for Nitrogen Heterocycles Based on Hydrogen Transfer Reactions

“…Subsequent intramolecular carbon-nitrogen bond formation would give the piperazine product. 16 After several experiments to obtain the optimized reaction conditions, they found that the reactions of anilines with alkanolammonium chlorides in the presence of a catalytic amount of a ruthenium catalyst (5-10 mol%) together with SnCl 2 ·2H 2 O (1 equiv.) in an aqueous medium (H 2 O-dioxane) at 180 o C for 20 h afforded the corresponding indoles in moderate to good yields.…”

“…Various vicinal-diols were subjected to react with o-phenylenediamines in order to investigate the reaction scope (entries [6][7][8][9][10][11][12][13][14][15][16][17][18][19][20]. The product yield was not significantly affected by the position of the substituent on the aromatic ring, whereas the electronic nature of that had some relevance to the product yield.…”

“…However, many functional groups were tolerated, including halide, nitrile, ester and furyl (entries [10][11][12][13][14]. Aniline could be used as the amine (entries [15][16][17] Aniline and other substituted anilines were reacted with 1,4-butanediol to give N-phenylpyrrolidines (entry 1-7), although the more electron poor anilines gave lower conversions under these conditions (entries 6 and 7). Aliphatic primary amines were also effective (entries 8-11), including the branched primary amine.…”

Highly Convenient and Large Scale Synthesis of 5-chloroindole and its 3-substituted Analogues

“…Similarly, ruthenium-catalyzed heteroannulation of anilines with alkanolammonium chlorides 13 or thermal cyclization of 4-chloroaniline with 1,2-dibromoethane 14 have also been reported. Recently, rhodium catalysed cycloisomerisation of 4-chloroanilines with trimethylsilyl acetylenes to obtain 5-chloroindoles was reported.…”