Synthesis of α,α′-asymmetric nitroxide radicals by C- or O-acylation of radical-enolate intermediates generated by reduction of homoallylic nitro enones with samarium(II) iodide

A new synthetic method to form two structurally different alpha, alpha'-asymmetric bicyclic nitroxides from the same substrate is described. Reduction of certain homoallylic nitro enones bearing a long alkyl chain with 3.0 equiv of SmI2 in THF at -78 degreesC gave a nitroxide radical-anion species of type A, while the same reduction followed by addition of HMPA at -78 degreesC resulted in the isomerization of the double bond to afford a different nitroxide radical anion species of type C. The former radical-anion undergoes O-acylation by the reaction with acyl chlorides to give alpha, alpha'-asymmetric bicyclic ester-nitroxides of type B, while the latter one does C-acylation to produce alpha, alpha'-asymmetric bicyclic beta -diketo nitroxides of type D.