THE TITANIUM-CATALYZED, ASYMMETRIC EPOXIDATION OF ALLYLIC ALCOHOLS WITH OPTICALLY-ACTIVE HYDROPEROXIDES IN THE PRESENCE OF ACHIRAL DIOL LIGANDS

The titanium-catalyzed, asymmetric epoxidation of dialkyl- and phenyl- substituted allylic alcohols with various enantiomerically pure hydrop eroxides has been examined in the presence of achiral diol ligands. En antioselectivities with ee values up to 50% were achieved in the oxyge n transfer from (-)-(S)-1-phenylethyl la and (-)-(S)-1-phenylpropyl 1b hydroperoxides to 3-methyl-2-buten-1-ol 2a and geraniol 2b in the pre sence of the diethyl 2-hydroxy-2-hydroxymethylmalonate (DHHM) as an ac hiral multidentate diol ligand. The DHHM additive was ineffective in t he asymmetric epoxidation of the phenyl-substituted allylic alcohols 3 c-f, and only low ee values (up to 15%) were obtained. The optically a ctive hydroperoxides (-)-(S)-1c and (-)-1d gave only moderate enantios electivities (ee values up to 24%) with or without the achiral malonat e additive DHHM. The concept of titanium-catalyzed, asymmetric epoxida tion with optically active hydroperoxides as oxygen donors in the pres ence of multidentate diols as achiral ligands is less effective in its enantioselectivity than the Sharpless modus operandi of employing t-b utyl hydroperoxide as achiral oxygen donor and the C-2-symmetric tartr ate as chiral auxiliary. (C) 1997 Elsevier Science Ltd.