From Diphenylcarbodiimide

The reaction product obtained from diphenylcarbodiimide and hydrogen cyanide is an intermediate in Sandmeyers indigo synthesis. HCN can also be eliminated from a-aminocarboxylic acid nitriles 589 to give l-cyano-N,N -disubstituted formamidines 590 and imines 591. ... 

Intermediate arylguanidinopyrimidines (285) produced from diphenylcarbodiimide and 5-alkyl(or aryl)amino-4-aminopyrimidines furnished 8-anilino-7-alkyl(or aryl)purines (286) in hot DMF (Scheme 101). 

Diphenylcarbodiimide can be stored for several weeks at 0°. At room temperature it gradually solidifies to a mixture of trimer and polymer. The monomer can be separated from the solid by vacuum distillation. 

Sandmeyer s valuable isatin synthesis involves the removal of sulphur from diphenylthiourea (I) (p. 169) with basic lead carbonate. Hydrogen cyanide is combined with the reactive diphenylcarbodiimide (II) so obtained, and the nitrile (III) produced is converted by means of hydrogen sulphide into tbe thioamide (IV). Concentrated sulphuric acid brings about ring closure and the product is the a-anil of isatin (V). Then, by hydrolysis with dilute sulphuric acid, aniline is removed ... 

Diphenylcarbodiimide can be prepared by the removal of the rlements of hydrogen sulfide from N,N -diphenylthiourea by... 

Cycloadducts derived from macrocyclic carbodiimides and diphenylcarbodiimide are also known (see Section 11.3.3). 

Similar adducts are produced from other cyclic diketones (see Table 2.4). N-pyridyl-(2)-triphenylphosphine imine 356 reacts with diphenylcarbodiimide via a [2+2] cycloaddition reaction. The initially formed cycloadduct 357 undergoes a cycloreversion reaction to give N-phenyl-N -pyridylcarbodiimide 358, which reacts with diphenylcarbodiimide to give a [2+4] cycloadduct 359 (yield 52%, mp 263-265 °C). ... 

Syntheses of triazinetriimines are reported isomelamines are prepared in 68-95% yield (see Section 6.12.9.2.2). A more general route is the cotrimerization of amines with cyanogen bromide high yields are recorded from readily available starting materials (see Section 6.12.9.5.1). Diphenyl-carbodiimide is trimerized by Lewis acids with phenol as promoter but the method is specific to diphenylcarbodiimide and not of general use. 

Guanidines are also obtained from carbodiimides (which are isomeric with cyanamides) since these react extremely readily with ammonia or amines. Thus, for instance, 7V,7V/,7V//-triphenylguanidine is formed exothermally when diphenylcarbodiimide is mixed with aniline.47 The analogous addition of phenylhydrazine to diphenylcarbodiimide, giving A,A -diphenyl-A"-(phenyl-amino)guanidine, forms the first step in the synthesis of nitrone.48... 

By addition of hydrogen chloride to diphenylcarbodiimide, Lengfeld and Stieglitz synthesized l-chloro-N,N -diphenylformamidine hydrochloride (XXII) in 1895. The reaction is not limited to diarylcarbodiimides, and from dialkylcarbodiimides the corresponding chloroformamidine hydrochlorides can be obtained in quantitative yield... 

Alkyl- and aryl carbodiimides can be prepared under mild conditions from thioureas with diethyl azodicarboxylate/triphenylphosphine (Mitsunobu reagent), typically in yields of around 80% the by-products are triphenylphosphine sulfide and diethyl hydrazodicarboxylate [1278]. The active intermediate in this system is the betaine 1739, which is formed from diethyl azodicarboxylate (DEAD) and triphenylphosphine. Driven by its charge distribution and its chalcogenophilicity, 1739 reacts with the thiourea 1740 to form the P,S bond in 1741. This energy-rich molecule stabilizes by decomposition into three molecules, namely the two byproducts, triphenylphosphine sulfide and diethyl hydrazodicarboxylate, and the desired carbodiimide 1699. Diphenylcarbodiimide 1699 (R = R = Ph) was prepared from N,N -diphenylthiourea 1740 (R = R = Ph) with DEAD and triphenylphosphine in 65% yield [1278]. 

Typical procedure. Diphenylcarbodiimide 1699 (R = R = Ph) [1278] Triphenylphos-phine (2.62 g, 0.01 mol) in THF (10 mL) was added dropwise to N,N -diphenyl-thiourea (2.28 g, 0.01 mol) and diethyl azodicarboxylate (1.74 g, 0.01 mol) in THF (20 mL) at room temperature. After standing overnight, the solvent was removed under reduced pressure and the residue was extracted with light petroleum (bp 30-60 °C) to separate soluble material from the remainder. The light petroleum extract was concentrated and distilled to give diphenylcarbodiimide bp 85-90 °C/ 0.2 mmHg, 1.27 g, 65%. 

Mixed dimers derived from macrocyclic carbodiimides and diphenylcarbodiimide are also reported. For example, the unstable 1,3-diazahepta-l,2-diene 15 (n = 4) was trapped with diphenylcarbodiimide to give the [2-1-2] cycloadduct 16 (n = 4). The larger ring cyclic carbodiimides also afford the [2-1-2] cycloadducts 16. These reactions proceed in quantitative yield... 

The CO insertion product is obtained in low yield. A similar reaction is observed with diphenylbutadiyne and diphenylcarbodiimide When the [2+2] cycloadduct derived from bis(trimethylsilyl)carbodiimide and a zir-conocene imide 32 is treated with diphenylacetylene a new metallacycle 33 is produced. Reaction of 33 with diisopropylcarbodiimide affords the six-membered ring metallacycle... 

A stable [3+2] cycloadduct 29 is also obtained from benzonitrile oxide and A-sulfonylaniline. On heating, the cycloadduct forms diphenylcarbodiimide and sulfur dioxide. This reaction is general and several 4,5-disubstituted 1,2,3,5-thiaoxadiazole 1-oxides 29 are obtained fromA -sulfonylaryl- and A-sulfinyl-alkylamines. ... 

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