Nitrogen substituted carbodiimides

Nitrogen substituted carbodiimides are usually not stable in the carbodiimide configuration. Some derivatives can be distilled under vacuum, but on standing they undergo slow dimerization reactions. In one case of N-heterocyclic carbodiimides the 1,3-diazetidine diimine dimers are obtained instead of the monomers. Semiempirical calculations on the formation of 1,3-diazetidine diimine dimers of H2N—N=C=NMe confirm the Z,Z and E,E configurations of the dimers obtained. N-nitrosubstituted carbodiimides are more stable. 

The infrared spectra of nitrogen substituted carbodiimides show the typical carbodiimide absorption at 2070-2090 cm  

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In the reaction of acylhydrazines with isothiocyanates, N-substituted thiourea derivatives 14 are formed, which react with a polystyrene based polymeric carbodiimide (PCD) to generate the nitrogen substituted carbodiimide 15, which cyclizes to form 2-amino-1,3,4-oxazoles 16. ... 

The remaining chapters are carbodiimides with unsaturated substituents, halogenated carbodiimides, acyl-, thioacyl- and imidoylcarbodiimides, silicon substituted carbodiimides, nitrogen substituted carbodiimides, phosphorous substituted carbodiimides, sulfur substituted carbodiimides, metal substituted carbodiimides, cyclic carbodiimides, polymeric carbodiimides and application of carbodiimides. 

Carbodiimides are a unique class of reactive organic compounds having the heterocumu-lene structure R—N=C=N—R. They can be formally considered to be the diimides of carbon dioxide or the anhydrides of 1,3-substituted ureas, and they are closely related to the monoimides of carbon dioxide, the isocyanates. The substituent R can be alkyl, aryl, acyl, aroyl, imidoyl or sulfonyl, but nitrogen, silicon, phosphorous and metal substituted carbodiimides are also known. The unsubstituted carbodiimide HN=C=NH is isomeric with cyanamide, H2NCN. Mono substituted carbodiimides, generated in the thermolysis of 1-substituted tetrazoles, can be isolated at liquid nitrogen temperature but isomerize to the cyanamides at higher temperatures. ... 

The boron substituted carbodiimides are stable liquids or solids, and the C signals of the center carbon atoms in boron carbodiimides are at 123-127.8 ppm. In the solid state, the boron substituted carbodiimides are almost planar, but the angle on the central carbon atom (127 °) and the nitrogen atoms (146 °, 163 °) show that the molecules are not strictly linear. ... 

In view of the importance in biochemical processes of pteridines such as folic acid, methotrexate, L-biopterin, and leucettidine <1996CHEC-II(7)679>, synthetic routes to fused pteridines continue to occupy considerable attention. Imidazo-fused pteridines have now been prepared from 3-aminopyrazine-2-carboxamides via carbodiimide intermediates. If the amido-nitrogen in the starting compound is further substituted, as in the scheme, the... 

The following brief summary is considered in more detail in the discussion of mechanism. Nitrogen 3 will normally be protonated as in uracil or unprotonated as in cytosine, serving as a hydrogen donor or acceptor, respectively. Substitution of any other function on this nitrogen atom invariably converts the normal base to a nonsubstrate component. This has been shown by Gilham (427) in the formation of a carbodiimide... 

The process is satisfactorily rationalized by the mechanism59 shown in Scheme 5, in which the hydrolytic formation of a substituted sulfenic add precedes that of the carbodiimide. Depending on the relative nucleophilidty of the sites in the thiourea, its condensation with carbodiimide will yield either the monosulfide (38d), by attack of sulfur on the carbodiimide (Path A), or the amidinothiourea (39d, Path B attack by nitrogen). The distribution... 

Curtius-type behaviour is followed on irradiation of the azide 610 at 10 K when methoxyisocyanate is obtained by migration of the methoxy group from carbon to nitrogen" . Carbamoyl azide is also photolabile under similar conditions and provides a route to aminonitrene The substituted amide derivative 611 also undergoes conversion to the corresponding isocyanate and, if this is brought about in the presence of carbodiimides, cycloaddition results in the formation of triazoles. ... 

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