Synthesis of Phospinamides in the 5,6-Oxaphosphabicyclooctene Series as Possible Precursors of Metaphosphoramidates

Article abstract of DOI:10.1021/jo00367a016

The readily dimerizable 1-aminophosphole oxides were found to function as dienes in the Diels-Alder reaction with N-phenylmaleimide, thereby providing phosphinamides with the 7-phosphanorbornene structure.The dimers also possess this structural feature, which has been subjected to the oxygen-insertion reaction with m-chloroperbenzoic acid.The Diels-Alder adducts react cleanly to provide the insertion product at the P-C bond, providing the 5,6-oxaphosphabicyclo<2.2.2>octene ring system; the dimers undergo reaction first at the phosphinamide nitrogen of the 2-phospholene ring and then at the 7-phosphanorbornene P-C bond.Stereochemical features of an aminophosphole oxide dimer and of the O-insertion product of a Diels-Alder adduct were unequivocally established by X-ray crystal structure analyses.The O-insertion occurred with retention of the configuration at phosphorus. 31P and 13C NMR spectra were also of value in structure assignments.The 5,6-oxaphosphabicyclo<2.2.2>octene prepared from the Diels-Alder adduct was completely decomposed by loss of the bridging phosphorus on heating in toluene at 100 deg C for 30 h.On the assumption that the fragment may be a metaphosphoramidate, trapping experiments with cyclohexanol and benzylamine were attempted.Only the latter gave a phosphorylation product, but since it greatly increased the rate of phosphorus debridging, it must be directly involved in a process that causes the ejection of the bridge.Intermediates in this process were detected by 31P NMR.