Pictet-Spengler condensation reactions catalyzed by a recyclable H+-montmorillonite as a heterogeneous Brønsted acid

Aqueous Synthesis of 1-H-2-Substituted Benzimidazoles via Transition-Metal-Free Intramolecular Amination of Aryl Iodides

“…Notably the use of water as solvent has attracted much attention in recent years [ 51 , 52 , 53 , 54 ]. In parallel with our efforts to develop metal-free synthetic protocols for the production of pharmaceutical and agrochemical heterocyclic compounds [ 55 , 56 ], we envisaged the application of more sustainable protocol to the aqueous synthesis of the benzimidazole framework under transition metal-free conditions.…”

Heterogeneous Catalysts in Pictet‐Spengler‐Type Reactions

“…On the other hand, solid acids or bases such as natural or modi�ed clays, zeolites, and mixed oxides have been used for various processes regarding organic synthesis in the search for environmentally friendly, economic processes which can be applied at industrial level. H + -montmorillonites and zeolites have been particularly used for this reaction [16][17][18].…”

o-Benzenedisulfonimide as a reusable acid catalyst for an easy, efficient, and green synthesis of tetrahydroisoquinolines and tetrahydro-β-carbolines through Pictet–Spengler reaction

“…For instance, tetrahydroisoquinolines show powerful anti-tumor, antimicrobial, anti-HIV activities; 1g-h tetrahydro-ßcarbolines are interesting hypnotic, anxiolytic, antimicrobial, antiviral, anti-tumor and anti-convulsant compounds. 1i Usually, Brønsted acids (recent examples are: H + montomorillonite, 2 trifluoroacetic acid, 1g,3 carboxylic acids-thiourea, 4 p-toluensulphonic acid, 5 perfluorooctanesulphonic acid in water, 6 chiral phosphoric acids 7 ) or Lewis acids (recent examples are: calcium complexes, 8 Yb(OTf) 3 , 9 AuCl 3 /AgOTf 10 ) are employed as catalysts to promote this reaction, involving the cyclization of iminium ions (or imines) resulting from the dehydration reaction of 2-arylethylamine derivatives with aldehydes.…”