4‘-Substituted-4-biphenylyloxenium Ions: Reactivity and Selectivity in Aqueous Solution
作者:Michael Novak、Matthew J. Poturalski、Whitney L. Johnson、Matthew P. Jones、Yueting Wang、Stephen A. Glover
DOI:10.1021/jo060198r
日期:2006.5.1
nucleophiles, and must be trapped by such nucleophiles via a preassociation mechanism. The second-order trapping that is observed in these two cases is enforced by the short lifetime of the cations, and may occur by a concerted SN2‘ mechanism or by internal azide trapping of an ion sandwich produced by azide-assisted ionization. Comparison of azide/solvent selectivities of the oxenium ions 1a−c with the corresponding
叠氮化物捕获表明,在4-芳基-4-乙酰氧基-2,5-环己二酮,2c和2d和O-(4-芳基)苯基-水解过程中产生了4'-取代的4-联苯基氧烯鎓离子1b - d。N-甲磺酰基羟胺,3b和3c。此外,4'-溴取代的酯,2d中,经过用N动力学上二次反应3 -即占叠氮化物加合物的一小部分,图5d。由于一阶和二阶叠氮化物捕获在2d中同时发生,二阶反应不受短寿命1d的影响,该寿命与未取代离子1a具有相似的叠氮化物/溶剂选择性。相比之下,即使18 O标记实验表明在水解二氯乙酸的部分过程中,二氯乙酸酯2e '和2f '的水解过程中叠氮化物捕集也无法检测到4'-CN和4'-NO 2离子1e和1f。两种酯都是通过C烷基-O键裂解而产生的。这些酯仅表现出叠氮化物的二级捕获。叠氮化物/溶剂选择性为1a - d的相关性与用于离子(Δ的水合所计算的相对的驱动力Ë当量4)来确定在所述PBP / DN * // HF / 6-31G