Catalyst- and Solvent-Dependent Stereodivergence in the Intramolecular Et<sub>2</sub>Zn/Pd<sup>0</sup>-Promoted Carbonyl Propargylation: Mechanistic Implications
作者:Mónica Arrate、Aritz Durana、Paula Lorenzo、Ángel R. de Lera、Rosana Álvarez、José M. Aurrecoechea
DOI:10.1002/chem.201301170
日期:2013.10.4
Carbonyl‐tethered propargylic benzoates undergo intramolecular carbonylpropargylation upon treatment with Et2Zn in the presence of a catalytic amount of Pd0 with the formation of 2‐alkynylcyclopentanol products. A ligand/solvent effect on the cis/trans selectivity (referring to the relative positions of alkynyl and OH groups) of ring‐closure has been found. In a non‐coordinating solvent (benzene),
羰基连接的炔丙基苯甲酸酯在催化量的Pd 0存在下,用Et 2 Zn处理后会发生分子内羰基炔丙基化,形成2-炔基环戊醇产物。发现了配体/溶剂对闭环的顺/反选择性(指炔基和OH基的相对位置)的影响。在非配位溶剂(苯)中,提高膦配体的供电子能力(同时降低其离解能力)会导致反式产物的增加趋势。另一方面,配位溶剂(THF)和PPh 3的组合,易于分解的膦,导致顺式产物的独家形成。实验和计算结果与烯丙基乙基钯中间体的不同行为兼容,该中间体在竞争性羰基加成和过渡金属化途径之间分配,每个途径导致不同的非对映异构体。这些结果还表明,膦的解离能力调节了该行为。