The unprecedented triarylcarbonium ion-pair-catalyzed Pictet–Spengler reaction of tryptamines with aromaticaldehydes and cyclic ketones in water was disclosed. Under metal-free conditions, diverse tetrahydro-β-carbolines and spirocyclic tetrahydro-β-carbolines were obtained in good yields with excellent functional group tolerance, including late-stage modification of natural products and small molecular
Comparative evaluation of a Pictet–Spengler protocol in microwave-assisted conversions of tryptamine with aryl- and carboxyaryl aldehydes: role of ring strain in cyclocondensation of the primarily formed carboxyaryl-substituted β-carbolines
An efficient microwave-assisted Pictet-Spengler protocol employing boric acid/acetic acid as a catalytic system was elaborated for the synthesis of 1-aryl-beta-carbolines. Under the novel conditions tryptamine and 2-formylbenzoic acid furnished a pentacyclic skeleton in a single step, whereas using o-phthalaldehyde as a coupling partner led to the formation of an isoindolone derivative. Three beta-carbolines primarily resulted from the reactions involving carboxy-substituted heteroaryl aldehydes and avoided cyclisation to polycondensed skeletons with enhanced ring strain, as was evidenced by density functional theory (DFT) modelling.
Selective construction of alkaloid scaffolds by alcohol-based direct and mild aerobic oxidative Pictet–Spengler reactions
Employing TBN/TEMPO as the catalysts and oxygen as the oxidant, the biologically and pharmaceutically significant tetrahydro-β-carboline and β-carboline alkaloid scaffolds that used to be obtained by multi-step processes can now be selectively obtained in only one-step via direct aerobicoxidative Pictet–Spengler reactions of tryptamines with alcoholsundermildconditions, with water generated as