Synthesis of Phosphinamides in the 5, 6-Oxaphosphabicyclo[2.2.2]octene Series as Possible Precursors of Metaphosphoramidates
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-phosphanorbomene 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 °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. © 1986, American Chemical Society. All rights reserved.
Quin, LD; Szewczyk, J; Szewczyk, KM; McPhail, AT
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