Enantiomerically pure tricyclic C-symmetric sulfide I can be prepared in high yield and only three steps from D-mannitol. When used in a one-pot sulfur ylide mediated epoxidation reaction, between 94 and 98% enantiomeric excess was obtained; the highest reported to date for the catalytic process. Molecular modelling studies of the ylide conformation provides a basis for understanding the stereochemical outcome of the reaction.