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, H-1, C-13 and Pt-195 NMR spectroscopies.