Departament de Química Física i Inorgànica. Universitat Rovira i Virgili, Campus Sescelades, C/Marcel·lí Domingo, s/n. 43007 Tarragona, Spain.
Org Biomol Chem. 2011 Feb 7;9(3):941-6. doi: 10.1039/c0ob00656d. Epub 2010 Dec 13.
We describe the application of a new class of ligands--the phosphite-oxazole/imidazole (L1-L5a-g)--in asymmetric intermolecular Pd-catalyzed Heck reactions under thermal and microwave conditions. These ligands combine the advantages of the oxazole/imidazole moiety with those of the phosphite moiety: they are more stable than their oxazoline counterparts, less sensitive to air and other oxidizing agents than phosphines and phosphinites, and easy to synthesize from readily available alcohols. The results indicate that activities, regio- and enantioselectivities, are highly influenced by the type of nitrogen donor group (oxazole or imidazole), the oxazole and biaryl-phosphite substituents and the axial chirality of the biaryl moiety of the ligand. By carefully selecting the ligand components, we achieved high activities, regio- (up to 99%) and enantioselectivities (up to 99%) using several triflate sources. Under microwave-irradiation conditions, reaction times were considerably shorter (from 24 h to 30 min) and regio- and enantioselectivities were still excellent.
我们描述了一类新型配体——膦酸酯-噁唑/咪唑（L1-L5a-g）——在热和微波条件下不对称分子间 Pd 催化 Heck 反应中的应用。这些配体结合了噁唑/咪唑部分和膦酸酯部分的优点：它们比恶唑啉更稳定，比膦和亚磷酸酯对空气和其他氧化剂更不敏感，并且易于从易得的醇合成。结果表明，活性、区域和对映选择性受氮供体类型（噁唑或咪唑）、噁唑和联芳基膦酸酯取代基以及配体中联芳基部分的轴向手性的强烈影响。通过仔细选择配体成分，我们使用几种三氟甲磺酸酯源实现了高活性、区域（高达 99%）和对映选择性（高达 99%）。在微波辐射条件下，反应时间大大缩短（从 24 小时缩短至 30 分钟），区域和对映选择性仍然优异。
