Triphenylphosphine Mediated Efficient Synthesis of 4-Substituted-1-methyl-2,5-dioxo-3-imidazolines

Summary.  Stable crystalline phosphorus ylides are obtained in excellent yields from the 1:1:1 addition reaction between 1-methylparabanic acid (1-methylimidazoline-2,4,5-trione) and dialkyl acetylenedicarboxylates in the presence of triphenylphosphine. These ylides exist in solution as a mixture of two geometric isomers. This is due to the restricted rotation around the carbon–carbon partial double bond resulting from conjugation of the ylide moiety with the adjacent carbonyl group. These ylides undergo smooth intramolecular Wittig reaction followed by an electrocyclic ring opening to produce dialkyl (E)-2-(1-methyl-2,5-dioxo-3-imidazolin-4-yl)-but-2-enedioates in good yields. Corresponding author. E-mail: isayavar@yahoo.com Received March 26, 2002; accepted (revised) April 24, 2002