Aryl-2,3-oxaphosphabicyclo[2.2.2]octene derivatives—the precursors of oxoarylphosphine oxides (aryl metaphosphonates)

The Baeyer–Villiger oxidation of 7-phosphanorbornene 7-oxides with sterically demanding substituents on the phosphorus atom () by m-chloroperbenzoic acid afforded the title products () as a mixture of two regioisomers ( and ). Isomer , the result of thermodynamic control, was stable, while isomer , the product of kinetic control, underwent decomposition and/or epoxidation. Single crystal X-ray analysis of P-(2,4,6-triisopropylphenyl) oxaphosphabicyclooctene () was not only useful in the evaluation of its structure, but, for the first time in the literature, a low-coordinated arylmetaphosphonate () formed by fragmentation on X-ray irradiation could also be detected. The precursors () were utilized in the thermoinduced and UV light-mediated fragmentation-related phosphorylations of alcohols. Beside the well-known elimination-addition mechanism via the metaphosphonate intermediate (), a novel addition-elimination route involving a species with a pentavalent pentacoordinated phosphorus atom () was also substantiated.