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Synthesis of 5H-pyrido[4,3-b]indole by a modification of Pomeranz-Fritsch isoquinoline synthesis
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1  Centro de Química, Universidade do Minho, Campus de Gualtar, 4710-057 Braga, Portugal

Abstract: 5H-Pyrido[4,3-b]indole was obtained from 3-formylindole in 16% overall yield by Jackson and Shannon modification of the Pomeranz-Fristch isoquinoline synthesis. The final cyclisation occurred but the removal of the tosyl group and oxidation of the dihydrocompound was not efficient. Changes in the concentration of the acid catalyst gave 29% as the best yield for the last step. An NMR study of the cyclisation is described.
Keywords: pyrido[4,3-b]indole, γ-carboline, isoquinoline, Pomeranz-Fritsch