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
当R(2)CHP(O)(NEt(2))OS(18)O(2)Ar(R(2)CH = 9-
芴基,Ar =
对甲苯基)经历亲核取代(消除加成)时, Et(2)NH(在CHCl(3)中为0.4 mol dm(-3))中,膦中间体R(2)C = P(O)NEt(2)与
磺酸盐离去基团重新结合(内部返回),导致加扰(18)O标签的扩散速度快于其扩散的速度;因此,向R(2)CHP(O)(NEt(2))(2)的有效转化取决于底物与亲核试剂之间的预缔合。