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Scope and limitations of ether-directed, metal-catalysed aza-Claisen rearrangements; improved stereoselectivity using non-coordinating solvents
Andrew G. Jamieson,Andrew Sutherland
Organic & Biomolecular Chemistry Pub Date : 06/30/2006 00:00:00 , DOI:10.1039/B607014K
Abstract

In an effort to understand and enhance the stereochemical outcome of the MOM-ether directed rearrangement of allylic trichloroacetimidates we have investigated various reaction conditions for this process. A range of Pd(II) and other metal catalysts have been shown to effectively catalyse the rearrangement providing the subsequent allylic amides in high selectivity (up to 11 : 1 ratio of diastereomers). The replacement of THF as a solvent in this reaction with non-coordinating solvents such as toluene has led to an enhancement of the directing effect resulting in a significant increase in the diastereoselective outcome (15 : 1 ratio). The reaction was also carried out for the first time, using a highly coordinating ionic solvent which disrupts binding of the Pd(II)-catalyst to the MOM-ether yielding the allylic amide in only moderate diastereoselectivity. These results provide further evidence for the ether directed aza-Claisen rearrangement of allylic trichloroacetimidates.

Graphical abstract: Scope and limitations of ether-directed, metal-catalysed aza-Claisen rearrangements; improved stereoselectivity using non-coordinating solvents
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