A highly regioselective direct C2-acylation of N-pyrimidine protected indoles with aldehydes is reported at room temperature through the merger of visible light photoredox and palladium(ii) catalysis. Late-stage acylation of tryptophan, selective mono-acylation of carbazole and the syntheses of tubulin inhibitors D-64131 and D-68144 are also demonstrated.
A palladium-catalyzed 1,2-carboamination through C-H activation at room temperature is reported for the synthesis of 2-arylindoles, and indolines from readily available, inexpensive aryl ureas and vinyl arenes. The reaction initiates with a urea-directed electrophilic ortho palladation, alkene insertion, and β-hydride elimination sequences to provide the Fujiwara-Moritani arylation product. Subsequently, aza-Wacker cyclization, and β-hydride elimination provide the 2-arylindoles in high yields. Intercepting the common σ-alkyl-Pd intermediate, corresponding indolines are also achieved. The indoline formation is attributed to the generation of stabilized, cationic π-benzyl-Pd species to suppress β-hydride elimination.
A ruthenium-catalyzed synthesis of 2-methylindole was accomplished via a C-H allylation/oxidative cyclization cascade. Strategically, β-hydride elimination from the σ-alkyl-Ru intermediate has been suppressed by steric hindrance from a remote position. Hence, 2-methylindolines from the corresponding ortho-substituted anilines were achieved via protodemetalation in lieu of β-hydride elimination under a modified reaction condition. This mild intermolecular annulation cascade proceeds smoothly by a redox-neutral ruthenium catalyst without stoichiometric metal oxidants, such as silver(I) or copper(II) salts, providing excellent functional group tolerance.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.