A Practical Indium Tribromide Catalysed Addition of Indoles to Nitroalkenes in Aqueous Media

Marco Bandini; Paolo Melchiorre; Alfonso Melloni; Achille Umani-Ronchi

doi:10.1055/s-2002-31970

PAPER

A Practical Indium Tribromide Catalysed Addition of Indoles to Nitroalkenes in Aqueous Media

Marco Bandini*, Paolo Melchiorre, Alfonso Melloni, Achille Umani-Ronchi*
Dipartimento di Chimica ‘G. Ciamician’, Università di Bologna, Via Selmi 2, 40126 Bologna, Italy
Fax: +39(51)2099456; e-Mail: bandini@ciam.unibo.it, umani@ciam.unibo.it;

Abstract

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Abstract

The 1,4-conjugate addition of indoles to nitroalkenes was efficiently carried out in aqueous media using a catalytic amount of indium tribromide (5 mol%). The reusability of the indium tribromide was tested by performing consecutive cycles with the same catalyst.

Key words

alkaloids - catalysis - indium - indoles - Michael additions

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References

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8 Recently, Yadav et. al. reported that InCl₃ (10 mol%) was also able to promote the conjugate addition of indole 5b to 6a in 78% yield using CH₂Cl₂ as the solvent. However, only one example of conjugate addition to nitroalkenes was described, see: Yadav JS. Abraham S. Reddy BVS. Sabitha G. Synthesis 2001, 2165. Under our conditions, InCl₃ was found less effective in comparison to InBr₃ in the addition of 5a to 6a, 82% yield

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Other common Lewis acids were found to be less effective in term of chemical yields and reaction times (i.e. AlCl₃, 68% yield, 24 h).