Microwave-assisted [2 + 3] cycloaddition of nitrones to platinum-(II) and -(IV) bound organonitriles

The coordinated EtCN in the anionic platinum(II)[Ph3PCH2Ph][PtCl3(EtCN)], the neutral platinum(II)[PtCl2(EtCN)2] or the neutral platinum(IV)[PtCl4(EtCN)2] complexes undergo [2 + 3] cycloadditions with cyclic non-aromatic nitrones and these reactions are greatly accelerated by microwave irradiation, to give, with a high stereoselectivity, complexes with bicyclic fused oxadiazolines as a racemic mixture in 60-90% yields, while acyclic nitrones are much less reactive and give a mixture of two diastereoisomers in the ratio 1 1. The new bicyclic oxadiazoline ligands can be liberated by reaction with a diphosphine. However, with a cyclic aromatic nitrone no cycloaddition is observed and only the product of the nitrile substitution is obtained. All compounds were characterised by elemental analyses, IR, 1H, 13C and 195Pt NMR spectroscopies.