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Efficient Synthesis of 4,4‘-Bi-1H-imidazol-2-ones from 5-Amino-α-imino-1H-imidazole-4-acetonitriles and Isocyanates
journal contribution
posted on 2002-06-27, 00:00 authored by Alice M. Dias, Isabel Cabral, M. Fernanda Proença, Brian L. BoothReactions of 5-amino-α-imino-1H-imidazole-4-acetonitriles 1 with alkyl and aryl isocyanates led
to efficient syntheses of 5‘-amino-5-imino-4,4‘-bi-1H-imidazol-2-ones 3 formed by intramolecular
cyclization of the corresponding 5-amino-α-(N-alkyl/arylcarbamoyl)imino-1H-imidazole-4-acetonitriles 2. The cyclization occurs only slowly in solution but is considerably accelerated by the addition
of a catalytic amount of DBU (1,8-diazabicyclo[5.4.0]undec-7-ene). The reaction of the N-arylamidine
6b, the synthetic precursor of the imidazole 1b, with benzyl isocyanate also led to the formation of
4,4‘-bi-1H-imidazol-2-one 3b in quantitative yield. The imidazole intermediate 2b has been isolated
and found to be identical with the compound obtained by reaction of the imidazole 1b and benzyl
isocyanate. The N-arylamidine 6c (R = 4-NCC6H4) reacted with benzyl isocyanate in a similar
way, but the electrophilicity of the amidine carbon atom resulted in rapid hydrolysis of the
intermediate 7c leading ultimately to the isolation of the urea 9. The N-alkylamidines 6a and 6d
behaved differently in their reaction with benzyl isocyanate, and the major product isolated in
these reactions is again the urea 9.