dynamic 1h nmr study around the carbon–carbon double bonds and carbon–carbon single bonds in a particular phosphorous ylide and 2,5-dihydro-5,5-diaryl-2-thio-1h-imidazoles

stable crystalline phosphorus ylides are obtained in excellent yields from the 1:1:1 addition reactionbetween hydantoins or thiohydantoins and dialkyl acetylenedicarboxylates in the presence oftriphenylphosphine. these phosphoranes undergo smooth intramolecular wittig reaction followedby an electrocyclic ring opening to produce dialkyl (e)-2-(2,5-dihydro-5,5-diaryl-2-thioxo-1h-imidazol-4-yl)fumarates and 2,5-dihydro-5,5-diaryl-2-thio-1h-imidazoles in good yields. dynamiceffects were observed in the 1h nmr spectra of these compounds and were attributed to restrictedrotation around the carbon-carbon single bonds. rotational energy barrier (δg#) for their interconversionprocess of rotational isomers equals to (68.2 and 71.7) ± 2 kj mol-1.