Unsaturated Carbodiimides

carbodiimides with a C=N bond in conjugation to the cumulative system undergo [2-1-4] cycloaddition reactions with suitable dienophiles (see Section 5.3.1). 

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TABLE 7.32. SYNTHESIS OF UNSATURATED 5(4/T)-OXAZOLONES VIA CYCLIZATION OF a,P-DIDEHYDROAMINO ACIDS OR a,P-UNSATURATED CARBODIIMIDES... 

Unsaturated isocyanates 3 are converted into bis-unsaturated carbodiimides 4 using a phos-pholene oxide catalyst. ... 

The reaction of unsaturated iminophosphoranes 5 with arylisocyanates affords mono unsaturated carbodiimides 6. The compounds are stable at room temperature in acetonitrile solution, but they cannot be distilled under vacuum. 

Unsaturated carbodiimides 27, generated in situ, can also be trapped with azo compounds to form 28 or with imines to give 29 via a [2+4] cycloaddition reaction. ... 

For more examples of polymers derived from unsaturated carbodiimides see Section 12.4. 

Unsaturated carbodiimides also undergo oligomerization reactions. An example is the cyclodimerization of dipyridyl-(2)-carbodiimide 37. This carbodiimide cannot be isolated because it undergoes dimerization via a [2+4] cycloaddition reaction to give the cyclodimer 38.5 ... 

An example of a [2+2] cycloaddition reaction across two carbodiimide groups generated in a pyrazole system is shown Section 3.2.3. However, unsaturated carbodiimides often react as azadienes in [2+4] cycloaddition reactions (for example in the preceding reaction). 

Ferrocenyl substituted unsaturated carbodiimides 56, generated in situ, undergo intramolecular cyclization to give heterocyclic substituted ferrocenyl derivatives 57. ... 

The pyridine ring system has also been obtained via the [4 -I- 2] cycloaddition reaction between enamines and acyclic azadienes like a,/3-unsaturated carbodiimides . In this way, compounds like 297 (obtained from the vinyliminotriphenylphosphorane 296... 

Cycloaddition. Unsaturated carbodiimides and aUcynes are combined to afford bicyc-lic amidines, under the influence of (C2H4)2RhCl2 and an aminodialk ox3fphosphine ligand. ... 

Cycloadditions The [4+2] cycloaddition reactions of carbodiimides with phenyl-carbonyl isocyanate, phenylcarbonyl isothiocyanate and thiocarbamoyl isothiocyanate have been discussed above. In the dimerization reactions the functional carbodiimides react as both the diene and the dienophile. Unsaturated carbodiimides, generated in situ, can be trapped with N=N bond- or C=N bond-containing substrates. 

Several intramolecular cyclization reactions of unsaturated carbodiimides are known and examples are listed in Table 3.18. 

Table 3.18 Intramolecular cyclization reactions of unsaturated carbodiimides Carbodiimide Cycloadduct Reference...

Unsaturated carbodiimides 232, generated in situ, can be trapped via an intermolec-ular [4+2] cycloaddition reaction using azo esters or imines to form 233 and 234,... 

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