Katsuki-type catalyst

Most of the oxidants used with these catalysts tend to be water soluble. However, the use of tetrabutylammonium monopersulfate (5) has been reported to provide relatively smooth oxidation with good ee s e.g, 4 -> 6) under monophasic conditions in organic solvents. The enantioselectivity is both substrate and catalyst dependent, with best results being obtained from electron-rich alkenes and Katsuki-type catalysts (c/. 2) <99TL1001>. Che and co-workers <99CC1789> have also reported on the use of an immobilized chromium binaphthyl catalyst, which offers the advantage of simple work-up and catalyst recovery. 

Comparable results were achieved in the asymmetric epoxidation of dihydronaphthalene with the Katsuki-type catalyst 53 in [C4Ciim][PF6].[50] Again, higher reaction rates were observed in the presence of the ionic liquid and the overall stability of the catalyst appeared to be superior to that with... 

Scheme 5.7 Epoxidation of 1,2-dihydronaphtalene with a chiral Katsuki-type catalyst...

The unsymmetrical analog of a Katsuki-type salen ligand was attached to Merri-field s resin (1% cross-Hnked) yielding a catalyst (22) (Fig. 4.3) which showed good efficiency and selectivity in the asymmetric epoxidation of 1,2-dihydronaphtalene with good performance after several recycling steps [81]. Related complexes (23) immobilized on silica were recently disclosed by Seebach and coworkers (Fig. 4.3) [82]. 

Chiral Katsuki-type salen catalyst has been recycled several times following its use in a model epoxidation reaction of 1,2-dihydronaphthalene in an ionic liquid. The enantioselectivity was comparable to that in dichloromethane, but recovery of the catalyst was easier and the activity was higher.165... 

Smith and Liu <02CC886> have immobilized a Katsuki-type salen ligand by an ester linkage to Merrifield s resin to produce catalyst 7. In a test epoxidation of 1,2-dihydronaphthalene (8)... 

An alternative approach for the epoxidation of simple olefins has been developed by Pietikainen and co-workers and Katsuki and co-workers by using the Jacobsen-type catalysts (Fig. 23) and in situ addition of imidazole or N-methylimidazole (122,129). The highest cc-values obtained were 60 % for... 

Burrow et al. examined aziridination with chiral Mn(salen) in the presence of PhI=NTs, but no enantioselectivity was observed.160 However, Katsuki et al. reported that the aziridination of styrene with complex (52) showed moderate enantioselectivity, though the chemical yield was poor (Scheme 38).161 Remarkable improvements of both enantioselectivity (up to 94% ee) and chemical yield have been achieved by using a new type of Mn(salen) (53) as the catalyst.162... 

Investigations by both Katsuki and Che have highlighted the application of chiral Mn(III) salen complexes for asymmetric N-atom transfer reactions (Fig. 17) [79-81]. In the former case, the use of [Mn(salen)PF6] together with PhI= Ts affords modest product yields and enantiomeric ratios for amination of simple benzylic and allylic starting materials. A high-valent Mn imido species is presumed to be the active oxidant. Methodological and mechanistic studies conducted by Che have found that the same types of Mn(III) salen complexes will induce oxidative cyclization of sulfamate esters. Although these catalysts afford... 

Salen-type complexes are a fundamental class of compounds in coordination chemistry, known since 1933. They have been extensively studied, and more than 2500 have been synthesized. Interest in salen-type complexes intensified in 1990 when the groups of Jacobsen and Katsuki discovered the enantioselective epoxi-dation of unfiinctionalized alkenes using chiral Mn(5alen) complexes as catalysts. Since that time, an extremely wide variety of reactions catalyzed by salen complexes have been investigated. 

In biatyl synthesis, although transition metal catalyzed aryl-aryl crosscoupling reactions have been widely exemplified using Suzuki-type reactions, CDC reactions between sp C-H bonds leading to sp C-C bonds are scarce. In 2010, Katsuki reported an enantioselective CDC reaction between two naphthol moieties catalyzed by a chiral iron(salan) complex under aerobic oxidative conditions (Scheme 4.23). Using 4 mol% of the iron(salan) complex 23-A as the catalyst in toluene at 60 °C for 48 h, two different 2-naphthols were coupled and the cross-coupled derivatives were isolated with moderate yields (44-70%) and good ee (87-95%). It must be pointed out that the homocoupling derivatives are also obtained in low yields. 

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