THE GENERATION OF METAPHOSPHORAMIDATES BY FRAGMENTATION OF 2,3-OXAPHOSPHABICYCLO[2.2.2]OCTENE DERIVATIVES

Abstract

Phosphole oxides with N,N-diethylamino, N-mesitylamino and N-tert-butylamino substituents on phosphorus were generated in the presence of N-phenylmaleimide to give Diels-Alder adducts with the 7-phosphanorbornene framework. Products were characterized by ³¹P and ¹³C NMR spectroscopy, and in one case by ¹⁷O NMR spectroscopy. Insertion of oxygen into a P[sbnd]C bond of this strained cyclic system occurred smoothly on treatment with m-chloroperbenzoic acid. The resulting derivatives with the 2,3-oxaphosphabicyclo[2.2.2]octene ring system were characterized by ¹H, ³¹P, and ¹³C NMR spectroscopy. In the case of the N-mesityl derivative, two stable isomers were formed and separated by chromatography. The full structure of one isomer was established by X-ray diffraction analysis. The ring system was fragmented on heating in toluene (110°C, 22–48 hrs) or on irradiation (30–35°C, 254 nm, 24 hrs) with the release of the P[sbnd]O bridging unit as a metaphosphoramidate (RR′N[sbnd]PO.). In the photolytic method, these products were effectively trapped with ethanol to give derivatives of structure RR′N[sbnd]P(O)(OH)(OEt). When these phosphoramidates were formed by trapping of the thermally generated metaphosphoramidates, a second reaction occurred with the alcohol that caused displacement of the amine, possibly by an elimination-addition reaction involving ethyl metaphosphate.

Key Words:

• Phosphole oxides
• 7-phosphanorbornenes
• 2,3-oxaphosphabicyclo[2.2.2]octenes
• N,N-diethyl metaphosphoramidate
• N-mesityl metaphosphoramidate
• N-tert-butyl metaphosphoramidate
• metaphosphates.