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Synthesis 2009(23): 4010-4014  
DOI: 10.1055/s-0029-1217052
PAPER
© Georg Thieme Verlag Stuttgart ˙ New York

Microwave-Assisted Solid-Acid-Catalyzed Friedel-Crafts Alkylation and Electrophilic Annulation of Indoles Using Alcohols as Alkylating Agents

Aditya Kulkarni, Phong Quang, Béla Török*
Department of Chemistry, University of Massachusetts Boston, 100 Morrissey Blvd., Boston, MA 02125, USA
Fax: +1(617)2876030; e-Mail: bela.torok@umb.edu;
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Publikationsverlauf

Received 29 April 2009
Publikationsdatum:
19. Oktober 2009 (online)

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Abstract

Alcohols are considered environmentally benign alkylating agents since the only by-product generated in their reactions is water. Herein, we report a microwave-assisted Friedel-Crafts alkylation and electrophilic annulation of indoles using alcohols as alkylating agents. Alkylation of indoles using tert-butyl alcohol gives 3-substituted tert-butylindoles. A domino electrophilic annulation/aromatization­ of indoles using hexane-2,5-diol results in the formation of substituted carbazoles. The reaction is catalyzed by a strong, solid-acid catalyst montmorillonite K-10. The products were obtained in good yields and high selectivities.

Key words

alkylation - carbazoles - indole - tert-butyl alcohol - hexane-2,5-diol - montmorillonite K-10 - microwave heating - annulation

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11

While a minimal amount of solvent was used during the sample preparation and product isolation, the reaction itself occurred under solvent-free conditions. Thus, the complete process is not solvent-free.