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

Abstract

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.