A ser of silyl enol ethers and ketene acetals 1a-h with alpha-and/or beta-phenyl as well as all;yl substituents of different steric bull; has been submitted to the enantioselective catalytic oxidation by chiral (salen)Mn-III complexes 3. Highest conversions and best enantioselectivities have been obtained with bleach rather than iodosobenzene as oxygen source for the active oxo-metal species. With regard to substrate structure, ee values up to 89% have been achieved for enol ethers with short and unbranched alkyl substituents at the siloxy position. While beta-phenyl groups are beneficial for enantiofacial control, phenyl substituents a to the siloxy functionality result in lower ee values, while the diphenyl-substituted derivative Id displays the lowest stereoselectivity, The fact that beta- versus alpha-phenyl substituents exhibit not only differences in the magnitude but also in the sense (opposite absolute product configuration) of the stereoselectivity may be utilized as a valuable mechanistic probe to assess steric and electronic effects in the substrate and the catalyst as a function of the type and pattern of substitution Our results display that steric interactions between the substrate and the ore-metal complex are mainly responsible for the observed stereochemical preferences. Indeed, significantly increased enantioselectivities are achieved even for the remote siloxy group when bulkier derivatives are:employed. In contrast, primarily electronic effects operate in the (salen)Mn-III catalyst 3 since electron-donating groups in the 5,5' positions of the salicylaldehyde ligand afford higher ee values in this catalytic oxidation. The skewed side-on approach (trajectory b) of the substrate onto the oxo-metal catalyst is favored, the metallaoxetane mechanism adequately accounts for the observed enantioselectivities. Herewith a synthetically-valuable method for the preparation of optically active alpha-hydroxy carbonyl products 2 has been made available through the catalytic, enantioselective oxidation of the silyl enol ethers 1 by (salen)Mn-III complexes.