The stereoselective thermal rearrangement of chiral lophine peroxides

The thermal reaction of chiral 2-phenyl-4-(p-X-phenyl)-5-(p-Y-phenyl)-4-tert-butyldimethylsilylperoxy-4H-isoimidazoles (5b: X = CF₃, Y = OMe; 5c: X = CF₃, Y = F) was carried out in DMSO. The chiral 2-phenyl-5-(p-X-phenyl)-5-(p-Y-phenyl)-5H-imidazol-4-ones (4b: X = CF₃, Y = OMe; 4c: X = CF₃, Y = F) were quantitatively obtained in 50-60% enantiomer excess (ee). The mechanism for the reaction was proved to be stereoselective 1,5-phenyl migration. Although the sigmatropic 1,5-phenyl migration should be thermally allowed according to the Woodward-Hoffmann rule, the migration actually includes a stepwise process.