Scrambling of the label in a fluorenylphosphonamidic [18O]-sulfonate during dissociative nucleophilic substitution (elimination-addition): a measure of the importance of preassociation.
When R(2)CHP(O)(NEt(2))OS(18)O(2)Ar (R(2)CH = 9-fluorenyl, Ar = p-tolyl) undergoes nucleophilic substitution (elimination-addition) with Et(2)NH (0.4 mol dm(-3) in CHCl(3)) the phosphene intermediate R(2)C=P(O)NEt(2) recombines with the sulfonate leaving group (internal return), causing scrambling of the (18)O label, more quickly than it diffuses away; efficient conversion into R(2)CHP(O)(NEt(2))(2) therefore depends on preassociation between the substrate and the nucleophile.
Harger
Martin J P
MJ
Department of Chemistry, University of Leicester, UK. mjph2@le.ac.uk