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| - First Enantioselective Catalyst for the Rearrangement of AllylicImidates to Allylic Amides
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| - A series of Pd(II) complexes containing chiraldiamine ligands were investigated as asymmetriccatalysts for the rearrangement of allylic imidates to allyl amides.The best catalysts were cationsobtained by dechlorination ofdichloro[(S)-2-(isoindolinylmethyl)-N-methylpyrrolidine]palladium(II) (17) with silver salts inCH2Cl2. Catalyst 18 wasstudied thoroughly and shown by 1H NMRand X-ray crystallography analysis to be a C1symmetric dimer (Figure ). A series of relatedcatalysts 22−27 having various counterions andanionic ligands were also prepared and studiedas asymmetric catalysts for the rearrangement of allylicN-(4-trifluorophenyl)benzimidate 29toallylic benzamide 30 (eq 4). Rearrangement of29 in CH2Cl2 (48 h at 40 °C)in the presence of 5mol % of 18 affords (−)-30 in 69% yield and55% ee. Enantioselection is increased to 60% whenanisomerically pure sample of 18 is employed. Chemicalcorrelation of allylic benzamide 30 with(R)-norvaline established that (−)-30 has theR absolute configuration (Scheme ). Acyclization-induced rearrangement mechanism (Scheme ) requires that in the majorpathway the imidatenitrogen attacks the re face of the olefin with Pdcoordinated to the si face. These studiesconstitutethe first report of asymmetric catalysis of the rearrangement ofallylic imidates to allylic amides.However, significant hurdles remain to be overcome before theenantioselective rearrangement ofallylic imidates becomes a practical route to enantioenriched nitrogencompounds.
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