The Jacobsen–Katsuki Epoxidation and Its Controversial Mechanism

Abstract

Epoxidation reactions have been established as an important method for the formation of carbon-oxygen bonds. In 1980 Sharpless and Katsuki developed an enantioselective variant for allylic alcohols which is still one of the most elegant methods in asymmetric synthesis. ['] Over the last few years unfunctionalized olefins have also become the focal point of interest as substrates, yielding epoxides in high enantiomeric excess when the optically active (salen)manganese(III) complexes 1 designed byJacobsen and Katsuki are used."] The best selectivities are achieved with cis-alkenes; however, recently the epoxidation of olefins having tri-and tetrasubstituted double bonds has also been successful with enantiomeric excesses of over The oxidants of choice are iodosobenzene and sodium hypochlorite at room temperature as well as meta-chloroperbenzoic acid at -78 "C. The proposed mechanism of the JacobsenKatsuki epoxidation is based on investigations by Kochi et al. While the existence of analogous CrV -0x0 complexes has been established by X-ray crystallographic analysis, the more reactive MnV complexes could only be speculated on. Recently, however, Plattner et al. made an important contribution to the mechanistic understanding by proving such intermediates with electrospray tandem mass ~pectrometry.[~I

Strengths, Weaknesses, Opportunities and Threats: Computational Studies of Mn- and Fe-Catalyzed Epoxidations

“…As exemplified in Figure 3 for Mn(salen)-type catalysts, this type of mechanism develops in two steps: the first being the oxidation of the catalyst using a terminal oxidant (such as H 2 O 2 , TBHP or OCl -) and the second being the oxygen-transfer step to the olefinic substrate [45].…”

“…As shown in Figure 4, a number of possible reaction paths are possible [45]. These include the formation of a metallaoxethane intermediate (Figure 4a), a concerted mechanism (Figure 4b), the formation of a five-membered ring structure including a nitrogen or oxygen atom of a spectator ligand, such as salen, or porphyrin (Figure 4c,d, respectively), or the formation of a carbon radical intermediate (Figure 4e) [34].…”

Functionalization of the benzobicyclo[3.2.1] octadiene skeleton possessing one isolated double bond via photocatalytic oxygenation

“…This interpretation is in accordance with the mechanism of Jacobsen-Katsuki epoxidation, where the free double bond approaches the metal oxo complexes side-on. 21 Such an approach is promoted by the positive charge on the porphyrin.…”

Revalorization of Grape Seed Oil for Innovative Non-Food Applications

“…This reaction has been established as one of the most important methods for the formation of carbon-oxygen bonds [59]. Epoxides are highly reactive and versatile functional groups which are commonly used as precursors for alcohols, glycols, carbonyls, alkanolamines, substituted oleins, polyester polyurethanes, and epoxy resins [60,61].…”