Synthesis of nitrogen heterocycles via palladium-catalyzed intramolecular cyclization

First Heterogeneous Ligand‐ and Salt‐Free Larock Indole Synthesis

“…[7][8][9][10][11][12][13][14][15][16] Many of these methods have proven to be most powerful and are currently applied in the targetor the diversity-oriented synthesis of multifunctional indoles but, recently, the palladium-catalysed heteroannulation of 2-iodoanilines with internal alkynes known as the Larock indole synthesis ( Figure 1, route 1) has emerged as one of the most powerful synthetic procedures to provide access to 2,3-susbtituted indoles. [17][18][19][20][21][22] Benzofurans, isoelectronic to indoles, also show a variety of pharmacological properties and minor changes of their structure offer a high degree of diversity that has proven useful for the search of new therapeutic agents. [23][24][25][26][27][28][29][30][31] Although the benzofuran motif occurs less often in nature and offers less potential structural multiplicity, the broad spectrum of pharmacological activity of these heterocycles led nevertheless to the elaboration of concise and flexible synthetic methods useful in the production of specific structures.…”

Synthesis of fused indoles by sequential palladium-catalyzed Heck reaction and N-heteroannulation

“…The resulting mixture was stirred at ambient temperature (27 h 13 2.1.15. 2-Propen-1-yl 2-bromo-3-nitrobenzyl sulfone (21). To a solution of trifluoroacetic anhydride (0.64 mL, 4.53 mmol) and acetonitrile (10 mL) was added urea/ hydrogen peroxide 29 (UHP) crystals (565 mg, 6.00 mmol) and the mixture was stirred (20 min) at ambient temperature.…”

“…Poor yields of products has previously been reported using N-allyl N-(2-halo)benzylamines in intramolecular Heck reactions. 21,22 It is not unlikely that the initial s-complex, formed by oxidative addition of palladium(0) into the aryl-bromine bond in 16, is coordinated to the pendant amine, forming a relatively stable complex. [23][24][25][26] This effectively removes palladium from the catalytic cycle, and the reaction is quenched.…”

First heterogeneously palladium-catalysed fully selective C3-arylation of free NH-indoles

“…8,9 These methods include the palladium-induced cycloadditions of 2-haloanilines with alkynes and the intra-or intermolecular reactions of 2-alkynyl anilides with aryl-or alkylhalides. 10,11 Other approaches are based on Heck-type cyclisations, 12,13 reactions of alkynes with imines 14 or on intramolecular cyclisations. Heteroannulation sequences achieved through palladium-catalysed aryl amination reaction were also reported.…”