Confirmation of chirality in homogeneous and heterogeneous salen-based catalysts

The extent to which diastereomeric excess (de) of epoxide products is influenced by the structure of the chiral olefin substrate has been assessed for two enantiomers of limonene and two enantiomers of pinene and using a number of homogeneous and heterogeneous [Mn(salen)]-based catalysts, based on both chiral and achiral structures. No evidence was obtained to suggest that double asymmetric induction took place, but instead results indicate that the stereoselectivity of the epoxide product was governed wholly by the substrate. Results call into question the use of such substrates alone in drawing conclusions regarding the nature of presumed stereogenic centers in such catalysts.