Manganese salen catalyst

An alternative preparation of aziridines reacts an alkene with iodine and chloramine-T (see p. 1056) generating the corresponding A-tosyl aziridine. Bromamine-T (TsNBr Na ) has been used in a similar manner." Diazoalkanes react with imines to give aziridines." Another useful reagent is NsN=IPh, which reacts with alkenes in the presence of rhodium compounds or Cu(OTf)2 to give N—Ns aziridines. Manganese salen catalysts have also been used with this reagent. ... 

The Jacobsen-Katsuki-catalysts (Fig. 13) have recently received much attention as the most widely used alkene epoxidation catalysts. An example of Jacobsen s manganese-salen catalyst is shown in Fig. 13. They promote the stereoselective conversion of prochiral olefins to chiral epoxides with enantiomeric excesses regularly better than 90% and sometimes exceeding 98%.82,89,92,93,128 The oxidation state of the metal changes during the catalytic cycle as shown in Scheme 8. 

Iron porphyrin catalysts with TBHP have been used for the diastereoselective oxidation of sulfides affording up to 46% d.e.408 A series of manganese(salen) catalysts with hydrogen peroxide has been employed for the oxidation of aralkyl sulfides in 34-70% d.e. and 80-90% yield. The best catalyst was derived from enantiomerically pure trans-1,2-diaminocyclohexane (Figure 3.101).409... 

Figure 3.101 Manganese salen catalyst for diastereoselective oxidation of sulfides with hydrogen peroxide.

Scheme 5.6 Epoxidation of 2,2-dimethylchromene with a chiral manganese-salen catalyst...

A highly enantioselective, low-temperature epoxidation of styrene has been disclosed by Jacobsen and co-workers using a chiral manganese salen catalyst and MCPBA as oxidant in the presence of NMO <94JA9333>. 

Immobilization of a sulfonated chiral manganese-salen catalyst on a fimctio-nalized Merrifield resin yielded a remarkably active epoxidation catalyst [42]. Its activity and enantioselectivity was examined by epoxidation of 6-cyanochromene, indene, styrene, 4-methylstyrene, and trans-stilbene using m-CPBA/NMO and quantitative yields were obtained in less than 5 min. Enantioselectivities were between 33% (4-methylstyrene) and 96% ee (6-cyanochromene). The same complex was also supported on silica and a layered double hydroxide (LDEI) and the catalytic performances of the systems were compared. Recycling experiments were carried out and the silica-based system showed metal leaching combined with a significant decrease in yield and ee. The layered double hydroxide- and resin-catalysts exhibited a slight decrease in activity and constant ee values in five consecutive reactions. 

Structurally related to the porphyrins, manganese salen catalysts have shown wide... 

Two recent examples of papain bioconjugation with formation of potential hybrid catalysts are shown in Figs. 6 and 7, featuring a manganese salen catalyst and dipyridyl complexes of copper, palladium, and rhodium, respectively [53, 58]. 

Imido and 0x0 compounds are intermediates in many of the transfers of oxygen atoms and nitrene units to olefins to form epoxides and aziridines, and they are intermediates in many of the insertions of oxygen atoms and nitrene units into the C-H bonds of hydrocarbons to form alcohols and amine derivatives. The enantioselective epoxidation of allylic alcohols (Scheme 13.22) " is the most widely used epoxida-tion process, and the discovery and development of this process was one of the sets of chemistry that led K. Barry Sharpless to receive the Nobel Prize in Chemistry in 2001. The mechanism of this process is not well established, despite the long time since its discovery and development. Nevertheless, most people accept that transfer of the oxygen atom occurs from a titanium-peroxo complex - rather than from an 0x0 complex. Jacobsen s and Katsuki s - manganese-salen catalysts for the enantioselective epoxidations of unfunctionalized olefins, which were based on Kochi s achiral chromium- and manganese-salen complexes, are a second set of... 

Chiral manganese salen catalysts have been widely used for the asymmetric oxidation of unactivated olefins. The dendritic polyglycerol-supported Mn-salen catalyst (44) was developed for the asymmetric epoxidation of the chromene derivative in a continuous membrane fiow reactor. This fiow system involves the continuous removal of the product (and unreacted substrate) from the high-molecular-weight dendritic catalyst (44) by filtration through a nanomembrane (Scheme 7.33). Under optimal conditions, 70% conversion with up to 92% ee was achieved [133]. In this system, however, the dendritic catalyst (44) worked as a homogeneous catalyst rather than a heterogeneous one. 

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