Katsuki-type complexes

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]. 

Jacobsen-Katsuki-type chiral (salen)cobalt(II) complex 267 (10 mol%) was used by Dunach and coworkers to catalyze electrochemical radical 5-exo cyclizations of ort/m-bromophenyl allyl ethers 293a,b to dihydrobenzofurans 295a,b (and 296a,b) [332]. Constant current or constant potential conditions... 

Kinetic resolution in the catalytic conversion of racemic chloro propanols to optically active epoxides has been achieved by use of a chiral Co(salen) type complex in combination with K2CO3. Although enantioselectivity was modest (< 35 % ee), this first use in asymmetric epoxide formation of the chiral ligand system that was later brought to fame through the Jacobsen-Katsuki asymmetric epoxidation is noteworthy [56,57]. When applied to the prochiral l,3-dichloro-2-propanol, asymmetric induction of up to ca. 60 % ee was achieved (Sch. 8) [58]. 

K. Smith, C.-H. Liu, Asymmetric epoxidation using a singly-bound supported Katsuki-type (salen)Mn complex, Chem. Commun. (2002) 886. 

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. 

Smith [199] involved immobilized Katsuki-type (salen)Mn complex 318 (R = H, Scheme 133) for the AE of 1,2-dihydronaphtalene with NaOCl/4-PPNO. The Katsuki-type (salen) 317 presenting an hydroxyalkyl group (R = CH2CH2CH2OH Scheme 133) on the 6-position was grafted onto a polystyrene resin via an ester link by means of polystyrene carboxyl chloride (1% crosslinked, 200-400 mesh, 1.17 mg/mol of chloride) (salen 319, Scheme 133). The counter ion seemed to have no influence on the catalytic efficiency and selectivity. For all of them, yields were about 40% with excellent ee (upper than 90%). Each catalytic system was reused after filtration, ee and yields remained quite imchanged. To increase the yield upon the recycle (up to 70%), concentration of the reaction mixture was required. 

Only a few years after the development of the homogeneous chiral Mn(salen) complexes by Jacobsen and Katsuki, several research groups began to study different immobiUzation methods in both liquid and soUd phases. Fluorinated organic solvents were the first type of Uquid supports studied for this purpose. The main problem in the appUcation of this methodology is the low solubility of the catalytic complex in the fluorous phase. Several papers were pubUshed by Pozzi and coworkers, who prepared a variety of salen ligands with perfluorinated chains in positions 3 and 5 of the saUcyUdene moiety (Fig. 2). 

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... 

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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