To unravel the origin of the stereocontrol in epoxidation reactions of unfunctionalized alkenes by diastereomeric biaryl oxaziridinium salts, two series of novel iminium cations were prepared. These moieties combine (Ra)-dimethylbiphenyl or (Ra)-5,5,6,6,7,7,8,8-octahydrobinaphthyl cores with chiral exocyclic appendages derived from commercially available (S)- or (R)-3,3-dimethylbutan-2-amine and (S)- or (R)-1-phenylpropan-1-amine. Under biphasic enantioselective olefin epoxidation conditions, in-situ generated bromide salts of these derivatives have displayed similar or better asymmetric efficiency than the classical binaphthyl derivatives. A structural analysis was performed in search of a correlation between the origin of the stereocontrol/level of enantioselectivity in the products, and dihedral angles around the biaryl twist of the catalysts.