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)