From Bisaryliminophosphoranes and Isocyanates or Isothiocyanates

The reaction of bisaryliminophosphoranes with di-t-butylcarbonate(Boc)20 in the presence of 4-dimethylaminopyridine, or carbon dioxide results in the formation of an intermediate isocyanate, which reacts with the second -N=PPh3 group to form a cyclic carbodiimide or a cyclic dicarbodiimide. Reaction of the bisaryliminophosphorane with carbon disulfide generates a bis-isothiocyanate which undergoes reaction with the bisaryliminophosphorane to give the corresponding cyclic dicarbodiimide in high yield. Examples of these reactions are listed in Tables 11.1 and 11.2. 

A heterocyclic ring annulated carbodiimide is generated from a bisaryliminophosphorane and trapped with phenyl isocyanate.  

When the bisaryliminophosphorane 32 is first converted with carbon disulfide into the corresponding diisothiocyanate 33 and subsequently reacted with another equivalent of the 

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