New Hybrid Ligands with a <i>trans</i>-1,2-Diaminocyclohexane Backbone: Competing Chelation Modes in Palladium-Catalyzed Enantioselective Allylic Alkylation
作者:Young Kook Kim、Seok Jong Lee、Kyo Han Ahn
DOI:10.1021/jo000821m
日期:2000.11.1
(up to 78% ee toward 14a and 80% ee toward 14b). Of particular note, dramatic changes in the sense and in the degree of the enantioselectivity were observed depending on the ligands and reaction conditions, which suggested a different chelation mode was competing with the supposed P,N-chelation mode. An X-ray crystal structure of a chelated palladium complex [Pd(3c)(eta(3)-PhCHCHCHPh)]PF(6) was obtained
从(1R,2R)-2-氨基环己基氨基甲酸叔丁酯(4)合成了三个具有反式1,2-二氨基环己烷骨架的新杂配体,该酯是通过对二胺的间接单保护而制备的。配体是(1R,2R)-N-2- [2-(二甲基氨基)苯甲酰基]氨基环己基-2-(二苯基磷基苯甲基)苯甲酰胺及其二正丁基氨基和二苯基氨基衍生物(3a-c),在金属螯合中可能具有较大的咬合角,从而形成正式的P,N型螯合物。为了评估针对已知的P,N-和P,P-螯合物(1和2)的新型杂合配体,将它们用于钯催化的两种标准外消旋烯丙基乙酸酯2-乙酰氧基-1,3之间的烯丙基烷基化反应。 -二苯基-2-丙烯(14a)和2-乙酰氧基-1、3-二甲基-2-丙烯(14b)和丙二酸二甲酯在不同的反应条件下。具有新配体的催化体系对具有适度对映选择性的两种底物均表现出良好的反应性(对14a的ee高达78%ee,对14b的ee高达80%)。特别值得注意的是,根据配体和反应条件,