ChemInform Abstract: Synthetic Studies on Indoles and Related Compounds. Part 49. Unexpected Formation of Quinolone Derivatives in Reissert Indole Synthesis.

Abstract

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Reissert Indole Synthesis Using Continuous-Flow Hydrogenation

“…The kinetic study of the reduction of the model compound o-nitrophenylpyruvate 1a was performed in classical batch mode [17] using Pd/C (5%) on 100-mg scale in EtOH (0.05 M) at room temperature under hydrogen atmosphere. The conversion was readily established by monitoring the composition of the reaction mixture by High Performance Liquid ChromatographyMass Spectrometry (HPLC-MS) analysis (Figure 1).…”

“…Structure of 5a and 6a were confirmed when the experiment was stopped after 1 h and product 5a and 6a were isolated in 29% and 63% yield, respectively. Alternative reduction approaches such as Zn/AcOH [15] and Pd-based heterogeneous catalytic hydrogenation either under hydrogen atmosphere [17] (both in batch and with continuous-flow mode) or using transfer hydrogenation with cyclohexene under microwave irradiation [19] have then been compared (Table 1). …”

Asymmetric cascade reaction of 2-nitrophenylpyruvates over chirally modified platinum catalyst

“…The transformation of 2-nitrophenylpyruvates using Zn + acetic acid or even heterogeneous Pd + H 2 leads to the formation of indole derivatives as reported by Reissert [34]. [33].…”

“…More than a decade ago in the reaction of 2-nitrophenylpyruvates over PtO 2 heterogeneous catalysts in H 2 atmosphere the formation of 3-hydroxy-3,4-dihydroquinolin-2(1H)-ones was observed by Murakami and co-workers [33]. The transformation of 2-nitrophenylpyruvates using Zn + acetic acid or even heterogeneous Pd + H 2 leads to the formation of indole derivatives as reported by Reissert [34].…”

“…If the first step is the reduction of the nitro group, the condensation of the formed amino and the keto group will lead to the usual indole derivative. However, if the hydrogenation of the -keto group occurs initially, the amino group formed by the consequent reduction of the nitro group may and will react with the ester moiety forming the racemic hydroxyquinolone derivative by intramolecular amidation [33].…”