B. Wang et al., EPIMERIZATION OF CYCLIC VINYLPHOSPHIRANE COMPLEXES - THE INTERMEDIACYOF BIRADICALS, Journal of the American Chemical Society, 118(7), 1996, pp. 1690-1695
The phosphinidene complex Ph-P-W(CO)(5) reacts with cyclopentadiene, 1
,3-cyclohexadiene, 1,3-cycloheptadiene, and 1,3-cyclooctadiene to give
in each case isomeric mixtures of syn- and anti-vinylphosphiranes. Wi
th longer reaction times and/or higher reaction temperatures, the anti
adducts isomerize to the syn adducts. These epimerizations are likely
to proceed via biradical intermediates. Only the syn-vinylphosphirane
of 1,3-cyclohexadiene undergoes a [1,3]-sigmatropic shift to yield a
syn-phopholene. The dichotomy of biradical and concerted mechanisms is
discussed in relationship with the analogous mechanism for the vinylc
yclopropane --> cyclopentene rearrangement.