Carbodiimides phenylcarbonyl isocyanate

The reaction of phenylcarbonyl isocyanate with carbodiimides at low temperatures affords oxazetidine imines 214 by addition across the OO bond of the isocyanate group. 

There is considerable discrepancy in the literature regarding the structures of the cycloadducts derived from carbonyl isocyanates and carbodiimides. For example, Arbuzov and Zobova " claim that a cycloadduct, mp 132-138 °C (dec.), derived from diphenylcar-bodiimide and phenylcarbonyl isocyanate at 0 °C has a diazetidinedione structure. Based on our findings an oxazetidine structure is indicated. 

Tsuge and Sakai obtain [2+4] cycloadducts 216 when the reaction of arylcarbonyl isocyanates with carbodiimides is conducted in refluxing benzene. Fom phenylcarbonyl isocyanate andN-phenyl-N -2-methylphenylcarbodiimide mixtures of [2+4] cycloadducts... 

Cycloaddition Reactions. In [2+2] cycloaddition reactions with car-bodiimides sometimes [2+4] cycloadducts are produced as coproducts. Examples include the reaction of phenylcarbonyl isocyanate, phenylcarbonyl isothiocyanate and thiocarbamoyl isothiocyanate with carbodiimides to give [2+4] cycloadducts, discussed in Section 5.3.1. In the current section, mainly [2+4] cycloaddition of carbodiimides as dienophile with dienes derived from oxoketenes, generated in situ or masked oxoketenes, especially 2,3-diones investigated by Kollenz and his coworkers are discussed. 

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. 

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