Synthesis of Aromatic (E)- or (Z)-α,β-Unsaturated Amides with Total or Very High Selectivity from α,β-Epoxyamides and Samarium Diiodide
José M. Concellón* and Eva Bardales
*Departamento de Química Orgánica e Inorgánica, Facultad de Química,
Universidad de Oviedo, Julián Clavería, 8, 33071 Oviedo, Spain, Email:
jmcguniovi.es
J. M. Concellón, E. Bardales, J. Org. Chem., 2003, 5, 9492-9295.
DOI: 10.1021/jo0349577
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Abstract
A highly stereoselective synthesis of aromatic α,β-unsaturated amides was achieved by treatment of aromatic α,β-epoxyamides with samarium diiodide. α,β-epoxyamides are easily prepared by the reaction of enolates derived from α-chloroamides with carbonyl compounds at -78°C.
Details
The document describes a highly stereoselective synthesis of aromatic (E)- or (Z)-α,β-unsaturated amides from α,β-epoxyamides using samarium diiodide (SmI2). The starting α,β-epoxyamides are prepared by reacting enolates derived from α-chloroamides with aldehydes or ketones at low temperatures. The process achieves total or very high stereoselectivity, producing (Z)-α,β-unsaturated amides from trisubstituted α,β-epoxyamides and (E)-α,β-unsaturated amides from di- and tetrasubstituted α,β-epoxyamides. The methodology is efficient and general, providing a valuable tool for organic synthesis, particularly in the preparation of natural products and compounds with biological and insecticidal activities. The document also proposes a mechanism involving the coordination of samarium with the oxirane ring, leading to the reduction and elimination steps that form the unsaturated amides. The described method complements previous work on the elimination of aromatic 2-chloro-3-hydroxyamides and offers a straightforward approach to synthesizing both (Z)- and (E)-α,β-unsaturated amides with high diastereoselectivity. The experimental section details the preparation of SmI2 and the procedures for synthesizing the epoxyamides and the final unsaturated amides, highlighting the efficiency and selectivity of the reactions.
Key Words
epoxyamides, unsaturated amides, reductive elimination, samarium diiodide
ID: J42-Y2003-1080