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 [PtCl 4 (MeCN) 2 ] and the nitrones - O + N(R 3 ) C(R 1 )(R 2 ) [R 1 = H, R 2 = Ph, o -C 6 H 4 OH, p -C 6 H 4 Me, p -C 6 H 4 OMe, p -C 6 H 4 NO 2, p -C 6 H 4 NMe 2, p -C 6 H 4 NMe 2 ·HCl, R 3 = Me; R 1 = H, R 2 = Ph, t Bu, R 3 = CH 2 Ph] proceeds smoothly under mild conditions and gives the first examples of Δ 4 -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 -[PtCl 4 (pyridine) 2 ]; subsequent workup allowed the isolation of the novel Δ 4 -1,2,4-oxadiazolines. All prepared compounds were characterized by elemental analyses, FAB or EI mass spectrometry, and IR and 1 H, 13 C{ 1 H}, and 195 Pt (metal complexes) NMR spectroscopies; X-ray structure determination was performed for the ( R, S ) diastereoisomer of