ChemInform Abstract: Synthesis, Fragmentation, and Photorearrangement of Neopentyl and Adamantyl Phosphonates in the 2,3-Oxaphosphabicyclo(2.2.2)octene System.

Abstract

Precursors for the generation of neopentyl and 1-adamantyl metaphosphates were prepared by the insertion of oxygen into a ring carbon-phosphorus 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 with retention of phosphorus configuration, but in one precursor with a syn-neopentoxy group a minor product from an inversion process was isolated. The 7-phosphanorbornene isomer with the uncommon anti neopentoxy 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 photochemical fragmentation of the precursors at room temperature to release the metaphosphates; these highly reactive species were trapped as phosphates when alcohols were inclued in the medium. Thermal fragmentation also was effective for generating the neopentyl ester. Irridiation was also performed at -75°C in an attempt to stabilize the metaphosphates so as to allow their spectral characterization, but a rearrangement occured to give a novel tricyclic compound. In this rearrangement, the ring oxygen shifted stereospecifically to the adjacent sp 2 carbon, and a cyclopropane ring was formed