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

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

References

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8

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.