Scope and limitations of ether-directed, metal-catalysed aza-Claisen rearrangements; improved stereoselectivity using non-coordinating solvents.
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.
Jamieson
Andrew G
AG
WestCHEM, Department of Chemistry, The Joseph Black Building, University of Glasgow, UK. andrews@chem.gla.ac.uk
Sutherland
Andrew
A