L. D. Quin, Xiao-Ping Wu, N. D. Sadanani, I. Lukeš, A. S. Ionkin, R. O. Day:
"Synthesis, Fragmentation, and Photorearrangment of Neopentyl and Adamantyl Phosphonates in the
J. Org. Chem. 59, (1994) 120-9
► DOI: 10.1021/jo00080a020, ► PDF
Precursors for the generation of neopentyl and 1-adamantyl metaphosphates were prepd. by the insertion of oxygen into a ring carbon-phosphorus bond of some
7-phosphanorbornenederivs. The stereochem. of the resulting products, which possess the 2,3-oxaphosphabicyclo[2.2.2]octenering system, was established by NMR spectroscopy, and by X-ray anal. in I (Np = neopentyl). The O-insertion(by MCPBA) generally proceeds 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-phosphanorborneneisomer II with the uncommon anti neopentoxy structure was synthesized by rearrangement of the syn isomer; O-insertiongave exclusively compd. III, the product of retention, identical to the minor product from the syn isomer. Conditions were developed for the photochem. fragmentation of the precursors at room temp. to release the metaphosphates [ROP(:O)2] (R = neopentyl, 1-adamantyl);these highly reactive species were trapped as phosphates when alcs. were included in the medium. Thermal fragmentation also was effective for generating the neopentyl ester. Irradn. was also performed at -75°Cin an attempt to stabilize the metaphosphates so as to allow their spectral characterization, but a rearrangement occurred to give a novel tricyclic compd., e.g., IV from photorearrangement of III. In this rearrangement, the ring oxygen shifted stereospecifically to the adjacent sp2 carbon, and a cyclopropane ring was formed.