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Copper-Catalyzed Synthesis of Tetrahydro-β-carbolines
Y. Ohta, S. Oishi, N. Fujii*, H. Ohno*
Kyoto University, Japan
22 June 2009 (online)
Reported are two direct synthetic routes to 1,2,3,4-tetrahydro-β-carboline derivates by one-pot domino three-component indole formation followed by a nucleophilic cyclization. Based on previous results (J. Bosch and co-workers J. Org. Chem. 1989, 54, 5591; Y. Murakami and co-workers J. Chem. Soc., Perkin Trans. 1 1999, 1717) the 2-(aminomethyl)indole 5 generated through a Mannich-type MCR via the plausible intermediate 4 by copper catalysis (N. Fujii and co-workers Angew. Chem. Int. Ed. 2007, 46, 2295) is converted into β-carbolines 6 (R³ = CH2OH) through a C3 cyclization induced by t-BuOK. The use of aminoester (R³ = CO2R) affords the 4-oxotetrahydro-β-carbolines 6 under acidic conditions.