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Review | Regular issue | Vol 91, No. 2, 2015, pp.239-264
Published online, 27th January, 2015
DOI: 10.3987/REV-14-811
Synthesis of Triazole, Indole, and Five or Six-Membered Saturated Heterocyclic Compounds

Yasunari Monguchi,* Yoshinari Sawama, and Hironao Sajiki*

*Laboratory of Organic Chemistry, Department of Pharmaceutical Sciences, Gifu Pharmaceutical University, 1-25-4 Daigakunishi, Gifu 501-1196, Japan

Abstract

Heterogeneously-catalyzed synthetic methods for the preparation of 1,2,3-triazoles, indolines, indoles, and saturated heterocyclic compounds, such as piperidine and pyrrolidine, are demonstrated. Triazoles are intermolecularly synthesized by the 1,3-dipolar cycloaddition of alkynes with azides using heterogeneous copper catalysts. Solvent-free triazole syntheses are also described. Inter- and intramolecular annulations as indole syntheses are summarized; e.g., a palladium on carbon (Pd/C)-catalyzed YamanakaLarock method affords 2- or 2,3-substituted indoles from 2-iodoaniline derivatives and mono- or di-substituted alkynes; an intramolecular Pd/C-catalyzed BuchwaldHartwig reaction of 2-bromophenethylamine derivatives temperature-dependently affords indolines or indoles. Pd/C can also catalyze an intermolecular aromatic amination of bromoarenes with indoles to generate the corresponding N-arylindoles. The application of the hydrogenation technology using 10% Pd/C, 10% rhodium on carbon (Rh/C), or 10% ruthenium on carbon (Ru/C) as a catalyst is finally introduced for the synthesis of indole by the intramolecular hydrogenative N-alkylation of 2-cyanomethylaniline and piperidine, pyrrolidine, and tetrahydrofuran derivatives by the arene hydrogenation of pyrridine, pyrrole, and furan derivatives under relatively mild conditions, respectively.