Highly Stereoselective 1,3-Dipolar Cycloaddition of Nitrones to (Nitrile)2PtII Species Furnishing Diastereomerically Pure 2,3-Dihydro-1,2,4-oxadiazole Ligands

Diastereomerically pure platinum(II) complexes 4−9 bearing tetrahydro-5,8-methanocyclohexa[3′,2′:4,5][1,3]oxazolo[3,2-b][1,2,4]oxadiazole ligands were generated under mild conditions (CH2Cl2, 20−25 °C, 24 h) by an intermolecular PtII-mediated 1,3-dipolar cycloaddition between enantiomerically pure camphor-derived oxazoline-N-oxides and the coordinated nitriles in the complexes trans-[PtCl2(R′CN)2] (R′ = Et, Ph, NMe2). These species were characterized by elemental analyses (C, H, N), high-resolution ESI+-MS, IR, 1H and 13C NMR spectroscopies, and also X-ray diffraction (for 5, 7, 8·CHCl3, and 9·Me2CO). Free heterocycles 10−13 were liberated as single stereoisomers from the (2,3-dihydro-1,2,4-oxadiazole)2PtII complexes (R = Et, Ph) by treatment with excess NaCN and were characterized by high-resolution ESI+-MS and 1H and 13C NMR spectroscopies.