Iridium‐Catalyzed Enantioselective Hydrogenation of Imines with Xylose Diphosphite and Diphosphinite Ligands

Abstract

Iridium complexes incorporating xylose diphosphinite 1 and diphosphite 2, 3 ligands as source of chirality are active catalysts for the hydrogenation of imines providing moderate ee. The enantioselectivity depends on the fine tuning of the structural parameters of the ligand and on the effect of additives.

New C2‐ and C1‐Symmetric Phosphorus Ligands Based on Carbohydrate Scaffolds and Their Use in the Iridium‐Catalysed Hydrogenation of Ketimines

“…This finding is in agreement with other reports and highlights the influence of the catalytic precursor on the enantioselectivity. [22,29] When shorter reaction times or lower temperatures (0°C) were used (Table 3, entries 2 and 3), the activity of the catalytic system and the optical yield decreased. After half an hour conversion was only 24 %, which gives a TOF of 48 h -1 (Table 3, entry 2).…”

“…However, there are only a few examples of rhodium and iridium complexes with chiral diphosphinite and diphosphite ligands used in the asymmetric hydrogenation of imines. [22,23] In this paper, we report the synthesis of a family of C 2 diphosphinite ligands 10a-d related to structure 7 (R = TBDPS) with different electronic properties, and the C 1 phosphinite/phosphite ligands 11a,b as a strategy for controlling the regio-or stereoselectivity in the iridium-catalysed asymmetric reduction of imines.…”

Synthesis of New Chiral Aryl Diphosphite Ligands Derived from Pyranoside Backbone of Monosacharides and Their Application in Copper‐Catalyzed Asymmetric Conjugate Addition of Diethylzinc to Cyclic Enones

“…[7] Further improvements of ligands of this type were achieved by Rajanbabu et al [8] Recently, new chelating chiral aryl diphosphite ligands, based on a furanoside backbone of glucose, were synthesized. These ligands gave good results in the Rh-catalyzed asymmetric hydroformylation of styrene, [9] Rh-catalyzed asymmetric hydrogenation, [10] as well as Pd-catalyzed asymmetric allylic substitution, [11] and up to 63% ee was obtained when these chiral ligands were used in the Cu-catalyzed asymmetric conjugate addition of diethylzinc to cyclic enones. [12] In this paper, we describe the synthesis of new chiral aryl diphosphite ligands based on the pyranoside backbones of glucose and galactose.…”

Application of Sugar-Based Phosphorus Ligands in Asymmetric Hydrogenation

“…配体 13～14 可由 D-木糖为原料合成, 将 它们用于底物为不饱和氨基酸的不对称氢化反应时可 高 ee 值得到产物, 实验结果发现金属催化剂的种类以 及糖基中 C-3 的构型对产物对映选择性有很大影响, 如 实验中用 Rh/配体 13 或者用 Ir/配体 14 时产物的 ee 值较 高, 但是用其它催化体系时产物 ee 值却很低. 配体 13 也被用于 Ir 催化的烯胺的不对称氢化反应中, 结果发现 产物的 ee 值为中等 [43] . 配体 15a 被成功用于 Rh 催化的 不饱和氨基酸的不对称氢化反应中(产物的 ee 值最高可 达 93%), 配体 15b 也被成功用于 Ir 催化的烯胺的不对 称氢化反应中(产物的 ee 值最高可达 70%) [22] .…”