Synthetic Approach To P=N Bond Formation Via The Condensation Of N-monosubstituted Arylurea And Ph₃P=O

Compounds containing P=N bond are generally known as phosphazene,which have extensive and important applications particularly in the organic synthesis,pharmaceuticals and biochemicals.Normally,in the synthetic organic field,phosphazene are versatile synthetic intermediates,which can be used for the reaction with carbonyl compounds,carboxylic acids,acyl halides.Furthermore,in the pharmaceuticals and biochemicals,Staudinger reaction has recently attracted renewed interest owing to the search for highly efficient bioorthogonal reactions.In recent years,iminophosphoranes?IPs?as protecting/directing groups for metal-mediated C-H bond activation reaction have been studied extensively.Therefore,the development of novel synthetic method for the formation of P=N bond is often desirable.The main contents are shown as follows:1.Through the improvement of the existing methods,we developed a one-pot reaction for the synthesis of N-monosubstituted urea with various anilines,H₂O,acetic acid glacial?HOAc?and KOCN?by added two times?at 45 ^oC,in yields of 50-95%.Moreover,the excess of HOAc switches the reaction towards the formation of N-monosubstituted urea.However,?-Substituted arylbiurets can be selectively prepared with excess amount of KNCO.2.In order to synthesize complex N-monosubstituted urea,a selective carbon-nitrogen coupling reaction has been developed.A DMEDA-promoted and copper-catalyzed approach has been designed for the coupling of aryl halides and chiral?-aminoamides to afford a range of functionalized chiral?-amino anilides?yield up to 96%?.This method leads to a higher yield and better reproducibility than those under ligand-free conditions.In addition,no racemization occurs,and the ee can reach to 99%.For certain hydroxyl-containing substrates,such as L-tyrosine amide and L-threonine amide,addition of a phase transfer catalyst?15-Crown-5?is necessary for such a transformation.3.The Hendrickson's reagent-mediated formation of the P=N bond,which lead to the synthesis of ArNHC?O?N=PPh3 with readily available N-monosubstituted arylurea and Ph3P=O in yields of 71-93%is described.In this transformation,the Hendrickson's reagent selectively reacts with the free amine group of N-monosubstituted arylurea rather than the oxygen on the same arylurea.Thioureas is a thionating reagent for the thionation of Ph₃P=O to Ph₃P=S.More importantly,this is a useful strategy for treatment of the troublesome Ph₃P=O.