Development of a Ruthenium‐Catalyzed Asymmetric Epoxidation Procedure with Hydrogen Peroxide as the Oxidant

Abstract

Novel pyboxazines and the known pybox ligands are used in the ruthenium‐catalyzed asymmetric epoxidation of olefins with H2O2 (see scheme). This new catalytic system is successful in the conversion of differently substituted aromatic olefins and gives ee values of up to 84 %.

Study of complexes of platinum group metals containing nitrogen bases derived from pyridine aldehydes: Interesting molecular structures with unpredicted bonding modes of the ligands

“…(1)eN(2) 76.98 (14), N(1)eRh (1)eCl (1) 87.67 (10), N(2)eRh (1)eCl (1) 93.81 (9), N(4)eRh (2)eCl (2) 87.54 (10), N(4)eRh (2)eO(2) 76.43(13), Cl (2)eRh (2)eO(2) …”

“…Crystals of complexes [4](PF 6 )$H 2 O, [6](PF 6 ) and [9](PF 6 )$H 2 O were mounted on a Stoe Image Plate Diffraction system equipped with a f circle goniometer, using Mo-Ka graphite monochromated radiation (l ¼ 0.71073 Å) with f range 0e200 . The structures were solved by direct methods using the program SHELXSe97 [44].…”

“…Such complexes have been prepared as part of studies in diverse areas such as inter-metallic communication [1], bioinorganic enzyme active site modeling [2], supramolecular approaches to chiral materials [3] and functional devices [4]. The organometallic chemistry of half sandwich complexes have been broadly developed in the past few decades, due to their wide range of potential applications as catalyst precursors for hydrogen transfer [5,6], ring opening metathesis polymerization [7,8] and olefin oxidation [9]. Arene ruthenium compounds have also been extensively investigated for their persuasive antibacterial and anticancer activity [10,11].…”

Metal‐catalyzed Synthesis of Epoxides

“…In their best result, with PhI(OAc) 2 as oxidant, they obtained trans-stilbene oxide in 80 % yield and with 63 % ee. More recently, Beller and coworkers have reexamined this catalytic system, finding that asymmetric epoxidations could be performed with ruthenium catalysts 29 and 30 and 30 % aqueous hydrogen peroxide (Table 6.11) [141]. Development of the pybox ligand provided ruthenium complex 31, which turned out to be the most efficient catalyst for asymmetric Scheme 6.20 olefin epoxidation, use of 5 mol % of 31 and slow addition of hydrogen peroxide allowing a number of aryl-substituted olefins to be epoxidized in yields of up >99 % and with enantioselectivities of up to 84 %.…”

Highly Diastereoselective Synthesis of 2,6‐Di[1‐(2‐alkylaziridin‐1‐yl)alkyl]pyridines, Useful Ligands in Palladium‐Catalyzed Asymmetric Allylic Alkylation

“…A significant niche in the domain of nitrogen ligands is held by N,N',N''-terdentate ligands, especially those having C 2 -symmetry. The pyridine ring is present in most compounds of this type (Figure 1), where it has the role of a spacer between two identical N-containing moieties, e.g., the widely used, high-performing pyridine-bis(oxazolines) 1 (Pyboxs) [2] as well as the more recently developed pyridine-bisA C H T U N G T R E N N U N G (oxazines) (Pyboxazines) ligands 2 [3] and pyridine-bis(imidazolidines) 3. [4] Both ligands 1 and 2 are readily prepared from 2,6-pyridinedicarboxylic acids and enantiopure b-and gamino alcohols, respectively, without the need to construct new stereocenters.…”