Diamino-4-cyanoimidazole

The formamidrazone (29) (1.01 g, 6.73 mmol) is dissolved in aqueous IM KOH (10 ml). A yellow solid soon precipitates. Filtration, washing with ether and drying as before gives the title compound (0.68 g, 82%), m.p. 214-215.5°C (dec.). 

The utility of urca.s and thioureas as substrates for making imidazoles is limited by the fact that the imidazole 2-substituent can only be an oxygen or sulfur function. Synthetic methods involving ureas and thioureas will also be discussed in Section 4.1, but some cyclizations of suitably functionalized species fall under the present heading. Appropriately substituted ureas and thioureas can be made from isocyanates and primary amines [36-38], from isocyanates and hydrazines [39] or thiocyanates and hydrazines [40], from or-aminonitrilcs and carbon dioxide [41] and by heating l,3,4-oxadiazol-2-oncs with amino acids [42]. Some of the substrates prepared in these ways, though, lead ultimately to reduced imidazoles such as hydantoins. Cyclizations arc usually acid catalysed, but they can also be thermal [43]. 

Suitable ureas have been prepared by treating 1-hydroxylamino- or 1-alkoxylamino-2,2-diethoxyethane with cyanic acid or an arylisocyanate, or by the addition of hydroxylamine (or an alkoxyaminc) to 2,2-diethoxyethylisocyanate. From the urea intermediates (30)-(32), 1- 

3-Butynylurea and the corresponding thiourea cyclize in sulfuric acid to form 4,5-dimethylimidazolin-2-one and the analogous 2-thione [43]. 

Acetylenic carbanilides cyclize and subsequently isomcrizc to 2(3H)-imidazolcthioncs and 2(3H)-imidazolones when treated respectively with hydrogen sulfide or potassium hydroxide in t-butanol. Although yields arc almost quantitative, this approach does not appear to be particularly convenient [49]. Mixtures of imidazoles and pyrazolcs are formed when phenacylcthylene ketal hydrazones of benzaldehyde and acetaldehyde are treated with aluminium chloride in benzene [50]. 

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Oxidation of Schiff bases of the monoamide 8 derived from diamino-maleonitrile gives 4-cyanoimidazole-5-carboxamides (Eq. 4). A new synthesis of 2-formyl-4-methyl-l-phenylimidazole 3-oxide (10) involves the fluoride-ion-promoted cyclization of the trimethylsilyl ether of JV-dichloro-acetyl-A-phenylaminopropanone oxime (9). ... 

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