Efficient Synthesis of 4,4‘-Bi-1<i>H</i>-imidazol-2-ones from
5-Amino-α-imino-1<i>H</i>-imidazole-4-acetonitriles and Isocyanates
Alice M. Dias
Isabel Cabral
M. Fernanda Proença
Brian L. Booth
10.1021/jo011192z.s001
https://acs.figshare.com/articles/journal_contribution/Efficient_Synthesis_of_4_4_-Bi-1_i_H_i_-imidazol-2-ones_from_5-Amino-_-imino-1_i_H_i_-imidazole-4-acetonitriles_and_Isocyanates/3691167
Reactions of 5-amino-α-imino-1<i>H</i>-imidazole-4-acetonitriles <b>1</b> with alkyl and aryl isocyanates led
to efficient syntheses of 5‘-amino-5-imino-4,4‘-bi-1<i>H</i>-imidazol-2-ones <b>3</b> formed by intramolecular
cyclization of the corresponding 5-amino-α-(<i>N</i>-alkyl/arylcarbamoyl)imino-1<i>H</i>-imidazole-4-acetonitriles <b>2</b>. 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 <i>N</i>-arylamidine
<b>6b</b>, the synthetic precursor of the imidazole <b>1b</b>, with benzyl isocyanate also led to the formation of
4,4‘-bi-1<i>H</i>-imidazol-2-one <b>3b</b> in quantitative yield. The imidazole intermediate <b>2b</b> has been isolated
and found to be identical with the compound obtained by reaction of the imidazole <b>1b</b> and benzyl
isocyanate. The <i>N</i>-arylamidine <b>6c</b> (R = 4-NCC<sub>6</sub>H<sub>4</sub>) reacted with benzyl isocyanate in a similar
way, but the electrophilicity of the amidine carbon atom resulted in rapid hydrolysis of the
intermediate <b>7c</b> leading ultimately to the isolation of the urea <b>9</b>. The <i>N</i>-alkylamidines <b>6a</b> and <b>6d</b>
behaved differently in their reaction with benzyl isocyanate, and the major product isolated in
these reactions is again the urea <b>9</b>.
2002-06-27 00:00:00
arylamidine 6 b
arylamidine 6 c
DBU
amidine carbon atom
benzyl isocyanate
urea 9
imidazole 1 b
NCC