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Synlett 2009(1): 122-126  
DOI: 10.1055/s-0028-1087386
LETTER
© Georg Thieme Verlag Stuttgart ˙ New York

Synthesis of 4-Acetoxyindoles and Related Derivatives by Means of Air Oxidation of 4-Oxo-4,5,6,7-tetrahydroindoles Obtained from Nitroalkenes and Cyclohexane-1,3-diones

Masaki Araia, Yayoi Miyauchib, Tadashi Miyaharab, Teruhiko Ishikawa*a,b, Seiki Saito*a
a Department of Medical and Bioengineering Science, Graduate School of Natural Science and Technology, Okayama University, Tsushima, Okayama 700-8530, Japan
Fax: +81(86)2517639; e-Mail: teruhiko@cc.okayama-u.ac.jp;
b Graduate School of Education, Okayama University, Tsushima, Okayama 700-8530, Japan
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Publication History

Received 28 July 2008
Publication Date:
12 December 2008 (online)

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Abstract

A novel method for synthesizing 4-hydroxyindole derivatives from cyclohexane-1,3-diones and nitroalkenes have been developed in which a newly developed air oxidation of 4-oxo-4,5,6,7-tetrahydroindoles is playing a crucial role.

Key words

indoles - cyclohexane-1,3-diones - nitroalkenes - Michael­ additions - oxidations

    References and Notes

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10

We are considering that transformation of I-A to I-C may involve an intermediary adduct I-B although nucleophilic attack of electron-rich dienamine function in I-A toward oxygen molecule, if any, might directly give I-C from I-A and could not be ruled out.

12

For general synthesis of cyclohexane-1,3-diones, see ref. 3a.


Table 5 Synthesis of 3-Substituted 4-Acetoxyindolines via Air
Oxidation

Entry Hydroindoles 10 Indoline 11 (yield, %)
1 10a

11a (59)
2 10b

11b (63)
3 10c

11c (28)
4 10d

11d (33)
5 10e

11e (54)
6 10f

11f (42)