SYNTHESIS, FRAGMENTATION, AND PHOTOREARRANGEMENT OF NEOPENTYL AND ADAMANTYL PHOSPHONATES IN THE 2,3-OXAPHOSPHABICYCLO[2.2.2]OCTENE SYSTEM

Precursors for the generation of neopentyl and 1-adamantyl metaphospha tes were prepared by the insertion of oxygen into a ring carbon-phosph orus bond of some 7-phosphanorbornene derivatives. The stereochemistry of the resulting products, which possess the 2,3-oxaphosphabicyclo[2. 2.2]octene ring system, was established by NMR spectroscopy, and by X- ray analysis in one case. The O-insertion (by MCPBA) generally proceed s with retention of phosphorus configuration, but in one precursor wit h a syn-neopentoxy group a minor product from an inversion process was isolated. The 7-phosphanorbornene isomer with the uncommon anti neope ntoxy structure was synthesized by rearrangement of the syn isomer; O- insertion gave exclusively the product of retention, identical to the minor product from the syn isomer. Conditions were developed for the p hotochemical fragmentation of the precursors at room temperature to re lease the metaphosphates; these highly reactive species were trapped a s phosphates when alcohols were included in the medium. Thermal fragme ntation also was effective for generating the neopentyl ester. Irradia tion was also performed at -75 degrees C in an attempt to stabilize th e metaphosphates so as to allow their spectral characterization, but a rearrangement occurred to give a novel tricyclic compound. In this re arrangement, the ring oxygen shifted stereospecifically to the adjacen t sp(2) carbon, and a cyclopropane ring was formed.