N,O-, N,N-, N,S-, and N,N,S-Heterocycles with an Exocyclic Amino Group in the Synthesis of 1,5,3,7-Diazadiphosphacyclooctanes

New 1,5,3,7-diazadiphosphacyclooctanes with N,O-, N,N-, N,S-, and N,N,S-heterocyclic substituents at the nitrogen atoms have been synthesized. The influence of the nature of amines containing sp(2)-hybridized nitrogen atom in the ortho-position of the heterocyclic substituent on the result of Mannich condensation in phosphine-paraformaldehyde-primary amine system has been revealed. The stabilization of intermediate acyclic products-aminomethyl(hydroxymethyl)arylphosphines and bis(aminomethyl)arylphosphines-due to amino-imine tautomerism is responsible for the low yield of the target cyclic diphosphines based on the above amines.