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Synthesis of 2-Aminopyrroles by Sequential MCR/[4+1] Cycloaddition
P. Fontaine, G. Masson*, J. Zhu*
Institut de Chimie des Substances Naturelles, Gif-sur-Yvette, France
25 May 2009 (online)
Reported is an efficient two-step synthesis of unsymmetrical polysubstituted 2-aminopyrroles from α,β-unsatured aldehydes. By combining a [4+1] cycloaddition with the oxidative three-component Strecker reaction developed previously by Zhu for the synthesis of α-iminonitriles 2 (P. Fontaine, A. Chiaroni, G. Masson, J. Zhu Org. Lett. 2008, 10, 1509), diversely substituted pyrroles 3 have been readily prepared. Indeed, after optimization of the [4+1] cycloaddition, a considerable number of aromatic and aliphatic isocyanides was studied, affording 2-amino-5-cyanopyrroles in good to excellent yield. However, in the presence of α-isocyanoacetamide 5, a Michael addition reaction occurred to afford the oxazole 6.