A New Class of Enehydroxylamino Ketones − (R)-2-(1-Hydroxy-4,4,5,5-tetraalkylimidazolidin-2-ylidene)ethanones: Synthesis and Reactions

Three approaches to the synthesis of (R)-2-(1-hydroxy-4,4,5,5-tetraalkylimidazolidin-2-ylidene)ethanones 1 are described: (a) condensation of 1,2-bishydroxylamines with β-ketoaldehyde synthons, (b) treatment of metallated 1-hydroxy-2-methyl-4,5-dihydroimidazoles with esters, and (c) 1,3-dipolar cycloaddition between 1-hydroxy-4,5-dihydroimidazole-3-oxide and DMAD. The reactivity of 1 with electrophiles has been studied. The exocyclic methylene (enamine) carbon atom is shown to be the major site of electrophilic attack. Synthesized chloro-substituted 1-hydroxy-2-acetylideneimidazolidines react with sodium cyanide to form the corresponding nitriles. Oxidation of these nitriles occurs with formation of persistent vinyl nitroxides, which are of interest as potential paramagnetic ligands. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)