Issue 5, 1990

Synthetic studies of indoles and related compounds. Part 22. The Vilsmeier–Haack reaction of N-benzyl-1,2,3,4-tetrahydrocarbazoles and its synthetic application to olivacine and ellipticine

Abstract

Vilsmeier–Haack reaction of 9-benzyl-1,2,3,4-tetrahydrocarbazole (18a) at 120 °C gave 9-benzyl-1-methylcarbazole-3-carbaldehyde (19a) and 9-benzyl-1 -[N,N-(dimethylamino)methyl]carbazole-3-carbaldehyde (22a) in moderate yields, whereas, the same reaction at 0 °C gave 9-benzyl-1,2,3,4-tetrahydrocarbazole-1-carbaldehyde (20a) in very good yield. The aldehyde (20a) was converted into 9-benzyl-1-methylcarbazole (21a) by another Vilsmeier–Haack reaction. This carbazole (21a) unexpectedly underwent non-regioselective formylation under similar reaction conditions to give a mixture of compound (19a) and 9-benzyl-8-methylcarbazole-3-carbaldehyde (23a). On the basis of the above results, a mechanism of the formation of the aromatic aldehyde (19a) was proposed, which involves 1,5-sigmatropic rearrangement of an N-methylidene dimethylammonium cation from the 4a-position to the 3-position as a key step. Vilsmeier–Haack reaction of 9-benzyl-1,2,3,4-tetrahydro-4-methylcarbazole (18b) at 100 °C also gave 9-benzyl-1,4-dimethylcarbazole-3-carb-aldehyde (19b) in moderate yield. The total syntheses of two antitumour alkaloids, olivacine (10) and ellipticine (11), were achieved by utilizing compounds (19a) and (19b) as key intermediates.

Article information

Article type
Paper

J. Chem. Soc., Perkin Trans. 1, 1990, 1319-1329

Synthetic studies of indoles and related compounds. Part 22. The Vilsmeier–Haack reaction of N-benzyl-1,2,3,4-tetrahydrocarbazoles and its synthetic application to olivacine and ellipticine

Y. Yokoyama, N. Okuyama, S. Iwadate, T. Momoi and Y. Murakami, J. Chem. Soc., Perkin Trans. 1, 1990, 1319 DOI: 10.1039/P19900001319

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