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

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.

addition reactions - alkaloids - heterocycles - indoles - lanthanides - Lewis acids - natural products

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