A Simple, Iron-Catalyzed, Pyridine-Assisted Hydrogen Peroxide Epoxidation System

Abstract

A simple and inexpensive system comprised of H 2 O 2 -pyridine-FeCl 3 · 6H 2 O for the catalysis of olefin epoxidation was established. Intriguingly, the reactivity of this system greatly depends on the amounts of pyridine. Various substrates, including aromatic and aliphatic olefins, were epoxidized by this simple system in moderate to excellent yields.Key words hydrogen peroxide; iron(III) chloride; olefin epoxidation; pyridine; acceleration Epoxides are highly desirable building blocks for the formation of fine chemicals, which are used in the production of pharmaceuticals, agricultural chemicals, industrial products or synthetic intermediates.1-3) Peracids are often used as oxidants. In particular, m-chloroperbenzoic acid (m-CPBA) has received considerable interest for use in the epoxidation of olefins to obtain the corresponding epoxides. [4][5][6] However, because of the cost, toxicity, and by-products of m-CPBA, a more cost-effective, harmless and clean oxidant is needed. Consequently, hydrogen peroxide has been extensively investigated as an alternative oxidant. Because hydrogen peroxide is safe and inexpensive, possesses a high oxygen content, and generates water as the only by-product, it is a viable candidate for use in epoxidation reactions. 7-10)Metal-catalyzed epoxidations with hydrogen peroxide results in outstanding yields.11-13) Nevertheless, although the superior metal catalysts like Re 14) or Pt 15,16) have excellent reactivity, the disadvantages of these metals cannot be ignored-namely, their high cost and quantitative insufficiency. Thus, our research focus has been on iron salts, which are relatively inexpensive compared with other transition metals, due to their natural abundance. Furthermore, iron salts have little risk to human health and are commercially available. [17][18][19][20][21] Beller and co-workers performed epoxidation of olefins in a reaction system comprised of FeCl 3 · 6H 2 O and H 2 O 2 , employing dipicolinic acid and an amine to activate the reaction. This method afforded the correspongding epoxides in good to excellent yields. [22][23][24][25][26] Recently, they also reported a simpler system that uses imidazole derivatives, rather than dipicolinic acid and amines, 27,28) as ligands. However, the reactivity of this system was moderate, and the ligands which resulted in relatively high yields had to be synthesized ad hoc before use because of commercial inavailability. Moreover its versatility regarding the use of different olefin substrates was limited. 27,28) We performed a more economical and practical H 2 O 2 -oxidized epoxidation of trans-stilbene 1 with a catalytic iron salt and a different ligand. This simple, FeCl 3 · 6H 2 O and pyridine combinative system catalyzed the reaction in excellent yield within only 30 min. In addition, this system was suitable for other substrates, such as aromatic and aliphatic olefins, both of which displayed good reactivity and excellent mass balance.At the onset of this work, a model catalytic epoxidation of trans-stilbene 1 was co...

Non-heme iron catalysts for epoxidation and aziridination reactions of challenging terminal alkenes: towards sustainability

“…Another FeCl 3 catalyzed non-enantioselective epoxidation of alkenes with hydrogen peroxide was reported by Ishizuka and co-workers. 75 The authors propose an iron(III)-pyridine complex as in situ generated catalyst, which shows greater activity than for example the iron(III)-(N-methyl)imidazole complex. However, pyridine is applied in high excess (2 equiv.)…”

Biomimetic Non-Heme Iron-Catalyzed Epoxidation of Challenging Terminal Alkenes Using Aqueous H2O2 as an Environmentally Friendly Oxidant

“…Even though the coordination structure of the most efficient catalyst was not provided, it was proposed that the peptide-based ligand bearing an N 2 O motif probably formed a biomimetic N 2 OFeCl 2 complex. Further catalytic approaches towards epoxide formation with non-heme iron complexes and H 2 O 2 or O 2 as environmentally friendly oxidants have been reported [19,20]. For example, in 2007 Beller and co-workers developed a remarkable method for the asymmetric epoxidation of aromatic alkenes using H 2 O 2 as oxidant [21,22].…”

Methyltrioxorhenium-Catalyzed Epoxidation of Homoallylic Alcohols with Hydrogen Peroxide

“…Epoxidation of alkenes is an important transformation because epoxides are valuable synthetic intermediates . Development of catalytic epoxidation methods using an environmentally benign oxidant such as hydrogen peroxide is currently of interest because it produces water as the only waste byproduct and has advantages of cost and atom efficiency. , Methyltrioxorhenium (MTO, CH 3 ReO 3 ) is one of the most efficient and well-studied epoxidation catalyst using hydrogen peroxide as the oxidant. Since the original finding of the properties of MTO as an epoxidation catalyst in 1991, a large number of studies related to MTO-catalyzed epoxidation have been reported. , …”