Arylcarbodiimides

Arylcarbodiimides also dimerize with alkyl phosphites (68CB174) and in special cases with triethylamine (76CC567). HBF4 is effective in giving the corresponding fluoroborate salts which can be converted to the bis(imino)-l,3-diazetidines with base (Scheme 87) (68AG(E)72, 72LA(762)167>. 

In the aromatic carbodiimides, the solid products are more stable than the liquid products. N-alkyl-N -arylcarbodiimides are less stable than diarylcarbodiimides. The introduction of electron attracting groups into the aromatic substituents seems to increase the polymerization tendency of the resulting carbodiimide. In contrast, electron donating substituents on the aromatic ring of arylalkylcarbodiimides enhance their reactivity with carboxylates.""... 

Steric as well as electronic factors determine the reactivity of carbodiimides. For example, N-alkyl-N -arylcarbodiimides with substituents R = NMe2 or Me in the p-position of the aryl group react faster than N-alkyl-N -arylcarbodiimides with R = NO2 in the p-position. ... 

Numerous N-2,4,6-trimethyl-3,5-dichloro-N -arylcarbodiimides are similarly obtained from the corresponding thiaoxadiazole 1-oxides in 60-80 % yield. " A bis-phenylene-... 

The reaction of carbodiimides with alkyl- or arylisocyanates proceeds exclusively across the C=N bond of the isocyanates to give 2-imino-l,3-diazetidine-4-ones 209 as evidenced by degradation studies In the case of N-alkyl-N -arylcarbodiimides the reaction proceeds... 

Cycloaddition Reactions Across C—C Multiple Bonds. Cycloadducts derived from carbodiimides and olefins or allenes are not known. However, the [2+2] cycloaddition of ketenes, R2C=C=0, to carbodiimides affords 4-imino-2-azetidinones (/3-lactames) 239 in high yield. Aliphatic carbodiimides show higher reactivity in comparison to aromatic carbodiimides, and the reaction proceeds across the aliphatic C=N bond in N-alkyl-N -arylcarbodiimides. The cycloadducts obtained in this reaction are listed in Table 2.3. 

Alkyl- and Arylcarbodiimides 63 Cp2Ti=C=CH2 intermediate are obtained in high yield. ... 

An intramolecular Diels-Alder reaction is observed on heating of suitably substituted arylcarbodiimides 362 to form the heterocycles 363.33 ... 

In the reaction of N-trimethylsilylmethyl-N -arylcarbodiimides 440 with ethylene glycol in the presence of a Cul catalyst mainly the isourea 441 is formed. ... 

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