FIRST ENANTIOSELECTIVE CATALYST FOR THE REARRANGEMENT OF ALLYLIC IMIDATES TO ALLYLIC AMIDES

A series of Pd(II) complexes containing chiral diamine ligands were in vestigated as asymmetric catalysts for the rearrangement of allylic im idates to allyl amides. The best catalysts were cations obtained by de chlorination of ndolinylmethyl)-N-methylpyrrolidine]palladium-(II) (II ) (17) with silver salts in CH2Cl2. Catalyst 18 was studied thoroughly and shown by H-1 NMR and X-ray crystallography analysis to be a C-1 s ymmetric dimer (Figure 1). A series of related catalysts 22-27 having various counterions and anionic ligands were also prepared and studied as asymmetric catalysts for the rearrangement of allylic N-(4-trifluo rophenyl)benzimidate 29 to allylic benzamide 30 (eq 4). Rearrangement of 29 in CH2Cl2 (48 h at 40 degrees C) in the presence of 5 mol % of 1 8 affords (-)-30 in 69% yield and 55% ee. Enantioselection is increase d to 60% when an isomerically pure sample of 18 is employed. Chemical correlation of allylic benzamide 30 with (R)-norvaline established tha t (-)-30 has the R absolute configuration (Scheme 3). A cyclization-in duced rearrangement mechanism (Scheme 1) requires that in the major pa thway the imidate nitrogen attacks the re face of the olefin with Pd c oordinated to the si face. These studies constitute the first report o f asymmetric catalysis of the rearrangement of allylic imidates to all ylic amides. However, significant hurdles remain to be overcome before the enantioselective rearrangement of allylic imidates becomes a prac tical route to enantioenriched nitrogen compounds.