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

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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• 5 Yanami T. Ballatore A. Miyashita M. Kato M. Yoshikoshi A. J. Chem. Soc., Perkin Trans. 1  1978,  1144 
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• 6a Leonarda P. Chiara G. Giacomo M. Maurizio T. Tetrahedron Lett.  2008,  49:  459 
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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)