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Synthesis 2003(3): 0397-0402
DOI: 10.1055/s-2003-37359
PAPER
© Georg Thieme Verlag Stuttgart · New York

A General Procedure for the Synthesis of 1,3-Bis(indolyl) Compounds via Michael­ Addition Catalyzed by InBr3/TMSCl

Marco Bandini*, Matteo Fagioli, 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; e-Mail: umani@ciam.unibo.it;
Further Information

Publication History

Received 4 December 2002
Publication Date:
19 February 2003 (online)

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Abstract

A new facile entry to the synthesis of 1,3-bis(indol-3-yl)butane-1-ones is presented. The procedure effectively utilizes a InBr3/TMSCl mixture (10 mol%) as a promoter for the chemoselective Michael addition of variously functionalised indoles to α,β-unsaturated indolyl ketones. The excellent yields and the mildness of the experimental conditions guarantee a widespread applicability of the protocol towards the construction of functionalised keto-bis(indolyl) compounds.

Key words

catalysis - enones - indium - indoles - Michael additions

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Benzothiophene and N-methylpyrrole were also reacted with 1a in the presence of InBr3/TMSCl (10 mol%) affording the corresponding 1,4-adduct in 18% and 72% yields, respectively. With N-methylpyrrole, the product was isolated as a 1:1 mixture of C-2/C-3 nucleophilic addition.

11

No Lewis acid/Lewis base interaction was detectable by 1H NMR (CD2Cl2, r.t.) analysis of a 1a/TMSCl mixture.