under mild conditions to give the corresponding ∆ 4 -1,2,4-oxadiazoline complexes cis-[PtCl 2 (R 3 MeSO)-{N᎐ ᎐ C(Ph)-ON(R 2 )-CH(R 1 )}] in 68-83% yield. In this reaction, the chiral sulfoxide in cis-[PtCl 2 (PhMeSO)(PhCN)] induces stereoselective formation of the coordinated ∆ 4 -1,2,4-oxadiazoline leading to mixtures of diastereomeric platinum complexes with a d.e. of 30-60%, which can be enhanced to >90% by fractional crystallization. The major diastereoisomer of [PtCl 2 (PhMeSO){N᎐ ᎐ C(Ph)-ON(Me)-C(H)Ph}] thus obtained was analyzed by X-ray diffraction and shown to have cis-(R,S ) configuration. Reaction of cis-[PtCl 2 (R 3 MeSO){N᎐ ᎐ C(Ph)-ON(R 2 )-CH(R 1 )}] with ethane-1,2-diamine results in displacement of the ∆ 4 -1,2,4-oxadiazolines from the metal and concomitant formation of water-soluble [Pt(en) 2 ]Cl 2 and sulfoxide, which can both be removed by aqueous extraction, and this allows for the first time the isolation of ∆ 4 -1,2,4oxadiazolines in enantiomerically enriched form. Applying this technique to cis-(R S ,S C )-[PtCl 2 (PhMeSO)-{N᎐ ᎐ C(Ph)-ON(Me)-C(H)Ph}] of 90% d.e. and 79% e.e. in sulfoxide, the corresponding (R)-2-methyl-3,5-diphenyl-∆ 4 -1,2,4-oxadiazoline was obtained with 70% e.e.Scheme 2 [2 ϩ 3] Cycloaddition of nitrones to [PtCl 2 (dmso)(PhCN)]