New Developments in Heterocyclic Chemistry of Phosphorus and Nitrogen

A series of phosphoric triamides of a general structure (R2N)3P=O has been prepared. The series included non-cyclic structures, as well as structures in which the phosphorus and two (monocyclic structure), or three (bicyclic structure) nitrogen atoms were incorporated in the five-membered heterocyclic ring. The molecular parameters (particularly the N-P-N bond angles and P-N bond distances) were determined by X-ray diffraction, and they were correlated with the 31P NMR shielding parameters of the phosphorus nucleus. A distinct interrelation between the NMR and crystal structure data was observed and interpreted in terms of the changes in the hybridization of the P-N bonding. In the next part, the chemistry of a new, bicyclic triamide system - 1-oxo-2,8-disubstituted- 2,5,8-triaza-1_5-phosphabicyclo[3.3.0]octane (3) was extensively studied. Solvolytic cleavage under acidic conditions yielded selectively a new, eight-membered monocyclic product (6), while the base-catalyzed reaction proceeded with the opposite selectivity, yielding the isomeric products (5). The most interesting observation was that products 6 undergo spontaneous rearrangement to the five-membered cyclic products 5. The mechanisms for the cleavage, and for the rearrangement, are discussed. Substrates 3 were also converted, through the lithiation-induced phosphorus migration from nitrogen to an aromatic carbon, to two new types of bicyclic phosphonic and phosphinic derivatives. The nucleophilic cleavage of the latter produced a new, twelve-membered cyclic phosphinic system containing three amine nitrogen atoms in the ring. Further studies on the selectivity in the cleavage of the new bicyclic systems are reported. Compounds 3 were finally used as starting materials for the preparation of the otherwise difficult to prepare triamines of the general structure ArNHCH2CH2NHCH2CH2NHAr (11). Amines 11 were in turn used as substrates for the preparation of the thiophosphoryl analogues of 3, the structure and chemistry of which is currently investigated.