Elimination–addition with alkylidineoxophosphorane (phosphene) intermediates in nucleophilic substitution at PO centres: fluoren-9-ylphosphonamidic chlorides with amine nucleophiles 1
作者:Martin J. P. Harger、Barbara T. Hurman
DOI:10.1039/a800683k
日期:——
Compared with Me2CHP(O)(NEt2)Cl, the fluorenyl compound R2CHP(O)(NEt2)Cl (R2CH = fluoren-9-yl) shows remarkably high reactivity in nucleophilic substitution with Et2NH. Substitution is catalysed by base 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU)} and shows little discrimination between competing Me2NH and Et2NH. These characteristics point to an eliminationâaddition (EA) mechanism with a reactive phosphene intermediate [R2CP(O)NEt2]. When Et2ND is the nucleophile, HâD exchange at the α carbon atom occurs much more quickly than substitution. This suggests that the elimination stage of the EA mechanism is reversible E1cB.
与 Me2CHP(O)(NEt2)Cl 相比,芴基化合物 R2CHP(O)(NEt2)Cl (R2CHÂ =Â fluoren-9-yl)在与 Et2NH 的亲核取代中显示出极高的反应活性。在碱 1,8-二氮杂双环[5.4.0]十一-7-烯(DBU)} 的催化下进行置换,在竞争的 Me2NH 和 Et2NH 之间几乎没有区别。这些特征表明,这种消去加成(EA)机理带有一个活性磷烯中间体[R2CP(O)NEt2]。当 Et2ND 为亲核体时,δ 碳原子上的 HâD 交换发生得比取代快得多。这表明 EA 机制的消去阶段是可逆的 E1cB。