[2 + 3] cycloaddition between acetonitrile ligands in the platinum(IV) complex [PtCl4(MeCN)(2)] and the nitrones -O+N(R-3)=C(R-1)(R-2) [R-1 = H, R-2 = Ph, sigma-C6H4OH, p-C6H4Me, p-C6H4OMe, p-C6H4NO2, p-C6H4NMe2, p-C6H4NMe2.HCl, R-3 = Me; R-1 = H, R-2 = Ph, 'Bu, R-3 = CH2Ph] proceeds smoothly under mild conditions and gives the first examples of Delta(4)-1,2,4-oxadiazoline complexes, [PtCl4{(N=C(Me)O-N(R-3)-C)(R-1)(R-2)}(2)], as a 1:1 mixture of two diastereoisomers. in 70-90% yields. The heterocyclic ligands were liberated almost quantitatively by reaction at room temperature of the complexes with a slight excess of pyridine in chloroform giving free (N=C(Me)O-N(R-3)-C)(R-1)(R-2) and trans-[PtCl4(pyridine)(2)]; subsequent workup allowed the isolation of the novel Delta(4)-1,2,4-oxadiazolines. All prepared compounds were characterized by elemental analyses. FAB or EI mass spectrometry, and IR and H-1, C-13{H-1}, and (195)pt (metal complexes) NMR spectroscopies: X-ray structure determination was performed for the (R,S) diastereoisomer of trans-[PtCl4{(N=C(Me)ON(Me)-C)H(p-C6H4OMe)}(2)].