Synthesis 2008(2): 320-324  
DOI: 10.1055/s-2007-990815
PSP
© Georg Thieme Verlag Stuttgart · New York

The CeCl3·7H2O/NaI/SiO2 System as an Efficient Promoter for the Friedel-Crafts Reaction of Indoles to Nitroalkenes under Solvent-Free Conditions

Giuseppe Bartolia, Giustino Di Antoniob, Sandra Giulib, Enrico Marcantoni*b, Mauro Marcolinib, Melissa Paolettib
a Dipartimento di Chimica Organica ‘A. Mangini’, Università di Bologna, v. le Risorgimento 4, 40136 Bologna, Italy
b Dipartimento di Scienze Chimiche, Università di Camerino, v. S. Agostino 1, 62032 Camerino (MC), Italy
Fax: +39(0737)402297; e-Mail: [email protected];
Further Information

Publication History

Received 13 February 2007
Publication Date:
25 September 2007 (online)

Abstract

The cheap, nontoxic and easy-to-handle CeCl3×7H2O/NaI Lewis acid promoter is optimal with regard to economic and ecological consideration and allows for useful applications in the synthesis of heterocyclic polyfunctionalized molecules. The procedure becomes efficient if the reaction is carried out under solvent-free conditions and on the surface of CeCl3×7H2O/NaI supported on silica gel. The simplicity of our method, especially that no precautions need to be taken to exclude moisture or oxygen from the reaction system, permit us to perform the Friedel-Crafts-type conjugate addition of indoles to nitroalkenes. The success of the reaction is independent of the type of indole or nitroalkene used, and provides 3-(2-nitroethyl)indolyl derivatives which are useful building blocks for the synthesis of various types of 3-(2-aminoethyl)indolyl derivatives. These can be subsequently transformed to the β-carbolines with different substituents.

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Generally, triflates are rather expensive and their use in large-scale synthetic methodology is very limited.