The titanium-catalyzed, asymmetric epoxidation of allylic alcohols with optically active hydroperoxides in the presence of achiral diol ligands

Article abstract of DOI:10.1016/S0957-4166(97)00101-8

The titanium-catalyzed, asymmetric epoxidation of dialkyl- and phenyl-substituted allylic alcohols with various enantiomerically pure hydroperoxides has been examined in the presence of achiral diol ligands. Enantioselectivities with ee values up to 50% were achieved in the oxygen transfer from (-)-(S)-1-phenylethyl 1a and (-)-(S)-1-phenylpropyl 1b hydroperoxides to 3-methyl-2-buten-1-ol 2a and geraniol 2b in the presence of the diethyl 2-hydroxy-2-hydroxymethylmalonate (DHHM) as an achiral multidentate diol ligand. The DHHM additive was ineffective in the asymmetric epoxidation of the phenyl-substituted allylic alcohols 3c-f, and only low ee values (up to 15%) were obtained. The optically active hydroperoxides (-)-(S)-1c and (-)-1d gave only moderate enantioselectivities (ee values up to 24%) with or without the achiral malonate additive DHHM. The concept of titanium-catalyzed, asymmetric epoxidation with optically active hydroperoxides as oxygen donors in the presence of multidentate diols as achiral ligands is less effective in its enantioselectivity than the Sharpless modus operandi of employing t-butyl hydroperoxide as achiral oxygen donor and the C₂-symmetric tartrate as chiral auxiliary.