Platinum(IV)-Assisted [2 + 3] Cycloaddition of Nitrones to Coordinated Organonitriles. Synthesis of Δ⁴-1,2,4-Oxadiazolines

[2 + 3] cycloaddition between acetonitrile ligands in the platinum(IV) complex [PtCl4(MeCN)2] and the nitrones -O+N(R3)C(R1)(R2) [R1 = H, R2 = Ph, o-C6H4OH, p-C6H4Me, p-C6H4OMe, p-C6H4NO2, p-C6H4NMe2, p-C6H4NMe2·HCl, R3 = Me; R1 = H, R2 = Ph, tBu, R3 = CH2Ph] proceeds smoothly under mild conditions and gives the first examples of Δ4-1,2,4-oxadiazoline complexes, 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 and trans-[PtCl4(pyridine)2]; subsequent workup allowed the isolation of the novel Δ4-1,2,4-oxadiazolines. All prepared compounds were characterized by elemental analyses, FAB or EI mass spectrometry, and IR and 1H, 13C{1H}, and 195Pt (metal complexes) NMR spectroscopies; X-ray structure determination was performed for the (R,S) diastereoisomer of