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Indoles - Sundberg R.J.

Sundberg R.J. Indoles - Academic press, 1996. - 95 p.
ISBN 0-12-676945-1
Download (direct link): indoles1996.djvu
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1. I. I. Grandberg, Т. I. Zuyanova, N, I, Afonia and T. A. Ivanova. Doklady Akad. Nauk, SSSR 176. 583 (1967); I. I. Grandberg, N. I. Afonia and Т. I, Zuyanova, Khim. Geterotsikl. Soedin. 1038 (1968).
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8. B. McKitirick, A. Faihli, R. J. Steffan, R. M. Soil, P. Hughes, J. Schmid, A. A. Asselin, С. C. Shaw, R, Noureldin and G. Gavin, J. Heterocycl. Chem, 27, 2151 (1990).
4. J, L. Castro, R, Bakei, A. R. Guiblin, S. C. Hobbs, M. R, Jenkins, M. G. N. Russell, M. S. Beer, .1. A, Stanton, K. Scholey, R. J. Haigreaves, М. I. Graham and V. G. Matassa, J. Med. Chem. 37, 3023 (1994).
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12. H. Yamamoto. J. Org. Chem. 32, 3693 (1967); H. Yamamoio, Chem. Pharm. Bull. 16, 17 (1968).
7.1.5 Anomalous reactions
Anomalous Fischer cyclizations are observed with certain o-substituted aryl-hydrazones, especially 2-alkoxy derivatives[l]. The products which are formed can generally be accounted for by an intermediate which would be formed by ipso-substitution during the sigmatropic rearrangement step. Nucleophiles from the reaction medium, e.g. Cl' or the solvent, are introduced at the 5-and/or 6-position of the indole ring. Even carbon nucleophiles, e.g. ethyl acetoacetate, can be incorporated if added to the reaction solution[2]. The use of 2-tosyloxy or 2-trifluoromethanesulfonyloxy derivatives has been found to avoid this complication and has proved useful in the preparation of 7-oxygen-ated indoles[3].
/pso-Substitution has also been observed with alkyl and aryl substituents and can lead to substituent migration. For example, 4-substituted indoles have been isolated from the cyclization of o-methyl and o-phenylphenylhydrazones of ethyl pyruvate. Formation of these by-products can be minimized by variation of the cyclization conditions and the use of p-toluenesulfonic acid in benzene or acetic acid was the preferred system[4],
I 1
1 H
Similarly, the iV-mesitylhydrazone of acetophenone gives 2-phenyl-4,5,7-trimethylindole as a minor product (10%)[5], 2,4,6-Trialkylphenylhydrazones have also been observed to give 5,6,7-trialkylindoles as the result of a formal 3a -► 6 shift[6]. These reactions probably occur via a 1,5-shift followed by a 1,2-shift.
_ CH3 C02C2H5
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3. Y. Murakami, H. Takabashi, Y. Nakazawa, M. Koshimizu, T. Watanabe and Y. Yokoyama Tetrahedron Lett. 30, 2099 (1989).
4. Y. Murakami, T. Watanabe, Y. Yokoyama, i. Naomachi, H. Iwase, N. Watanabe, M. Morihata, N. Okuyama, H. Kamakura, T. Takahashi, H. Atoda, T. Tojo, K. Morita and H. Ishii, Chem. Pharm. Bull. 41, 1910 (1993).
5. R. B. Carlin and J. W. Harrison, J. Org. Chem. 30, 563 (1965).
6. B. Miller and E. R. Matjeka, J. Am. Chem. Soc. 102, 4772 (1980).
7.1.6 The Japp-Klingemann route to arylhydrazones
The Japp-Klingemann coupling of aryldiazonium ions with enolates and other nudeophilic alkenes provides an alternative route to arylhydrazones. The reaction has most frequently been applied to P-ketoesters, in which deacylation follows coupling and the indolization affords an indole-2-carboxylate ester.
и ,CH2R x-Й- 'I co2R'
ArN2+ + R"CCHC02R' -*■ ArNHN=C
ch2r c°2r'
If, instead of an ester, the Japp-Klingemann reaction is done with a salt of a [5-ketoacid, decarboxylation occurs and the eventual product is a 2-acyl-indole.
9 ch2r ri^v4v
ArN2~ + '°2CCHCR' -► ArNHN=C -► ' SR'
CH2R nR i
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