The action of bromine on 5-unsubstituted 3,4-diphenyl-4-imidazolin-2-ones

Diphenylparabanic Acid as a Synthon for the Synthesis of α-Diketones and α-Ketocarboxylic Acids

“…Third, it may be possible to isolate intermediate, a certain cyclic hemiaminal, 7 produced by the reaction of 4 with a nucleophile, since it has been reported that certain N,N′,5-trisubstituted 5-hydroxyimidazolidine-2,4-diones are isolable. 15 First, we treated diphenylparabanic acid 4 with >2 equiv of phenyllithium (9a) in THF at −78 °C for 3 h. A usual workup of the reaction mixture gave 1,2-diphenylethane-1,2-dione (5a), as expected, in 84% isolated yield along with N,N′-diphenylurea. Similar treatment of 4 with 1-naphthyllithium (9b) or 2-naphthyllithium (9c) gave the corresponding 1,2-diarylethane-1,2-diones 5b and 5c in good yields, as shown in Table 1.…”

“…Second, a fixed cisoid −CO–CO– structure presumably stabilizes the metal salt of monoadduct 7 produced from organolithium or Grignard reagent by forming a chelate, so that it preferably inhibits side reactions such as a double nucleophilic attack on the same carbon. Third, it may be possible to isolate intermediate, a certain cyclic hemiaminal, 7 produced by the reaction of 4 with a nucleophile, since it has been reported that certain N , N ′,5-trisubstituted 5-hydroxyimidazolidine-2,4-diones are isolable …”