Evidence for the involvement of pentacoordinate P-intermediates during theUV light-mediated fragmentation of a 2-phosphabicyclo[2.2.2]octene 2-oxidein the presence of O-nucleophiles

Isotope-exchange experiments with (H2O)-O-18 proved at least the partial in volvement of a P(V)-species (8) as an intermediate in the UV light-promoted fragmentation of phosphabicyclooctene (1). Selection between the alcohols of equimolar mixtures during the photochemical fragmentation of 1 also sugg ests a mechanism where an adduct (4) is formed in the rate-determining step affording the phosphorylated product (5) after decomposition. We were able to prove that the transient adduct (4) is formed in a reversible manner. ( C) 2000 Elsevier Science S.A. All rights reserved.