Dias Alice M, Cabral Isabel, Proença M Fernanda, Booth Brian L
Departamento de Química, Universidade do Minho, Campus de Gualtar, 4710 Braga, Portugal.
J Org Chem. 2002 Aug 9;67(16):5546-52. doi: 10.1021/jo011192z.
Reactions of 5-amino-alpha-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-alpha-(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-NCC(6)H(4)) 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.
5-氨基-α-亚氨基-1H-咪唑-4-乙腈1与烷基和芳基异氰酸酯反应，能高效合成5'-氨基-5-亚氨基-4,4'-联-1H-咪唑-2-酮3，其由相应的5-氨基-α-(N-烷基/芳基氨基甲酰基)亚氨基-1H-咪唑-4-乙腈2分子内环化形成。环化反应在溶液中进行得很慢，但加入催化量的DBU（1,8-二氮杂双环[5.4.0]十一碳-7-烯）后会显著加速。咪唑1b的合成前体N-芳基脒6b与苄基异氰酸酯反应，也能定量生成4,4'-联-1H-咪唑-2-酮3b。咪唑中间体2b已被分离出来，发现其与咪唑1b和苄基异氰酸酯反应得到的化合物相同。N-芳基脒6c（R = 4-NCC(6)H(4)）与苄基异氰酸酯的反应方式类似，但由于脒碳原子的亲电性，中间体7c会迅速水解，最终分离得到脲9。N-烷基脒6a和6d与苄基异氰酸酯反应时表现不同，这些反应中分离出的主要产物同样是脲9。
