Aerobic oxidation asymmetric

Keywords Aerobic oxidation Asymmetric reduction catalyst Concerto catalysis Cooperating ligand... 

The complex Pd-(-)-sparteine was also used as catalyst in an important reaction. Two groups have simultaneously and independently reported a closely related aerobic oxidative kinetic resolution of secondary alcohols. The oxidation of secondary alcohols is one of the most common and well-studied reactions in chemistry. Although excellent catalytic enantioselective methods exist for a variety of oxidation processes, such as epoxidation, dihydroxy-lation, and aziridination, there are relatively few catalytic enantioselective examples of alcohol oxidation. The two research teams were interested in the metal-catalyzed aerobic oxidation of alcohols to aldehydes and ketones and became involved in extending the scopes of these oxidations to asymmetric catalysis. 

Bolm et al. (130) reported the asymmetric Baeyer-Villiger reaction catalyzed by Cu(II) complexes. Aerobic oxidation of racemic cyclic ketones in the presence of pivalaldehyde effects a kinetic resolution to afford lactones in moderate enan-tioselectivity. Aryloxide oxazolines are the most effective ligands among those examined. Sterically demanding substituents ortho to the phenoxide are necessary for high yields. Several neutral bis(oxazolines) provide poor selectivities and yields in this reaction. Cycloheptanones and cyclohexanones lacking an aryl group on the a carbon do not react under these conditions. 

In addition to the development of new catalysts and reaction conditions for aerobic oxidative heterocycUzation, considerable effort has been directed toward asymmetric transformations. Hosokawa and Murahashi reported the first example of asymmetric Pd-catalyzed oxidative heterocycUzation reactions of this type [157,158]. They employed catalytic [(+)-(Ti -pinene)Pd (OAc)]2 together with cocatalytic Cu(OAc)2 for the cycUzation of 2-allylphenol substrates however, the selectivity was relatively poor (< 26% ee). 

Chiral A-salicylidene vanadyl carboxylates are efficient catalysts for asymmetric aerobic oxidation of a-hydoxy esters and amides with divergent substituents. These catalysts have been explored for the kinetic resolution of secondary alcohols also. The stereochemical origin of the almost total asymmetric control has been probed.262... 

The possibility of asymmetric induction under the fluorous biphase conditions was first speculated upon by Horvath and Rabai [10], and this year has seen the first report of asymmetric catalysis in a fluorous biphase [69]. Two, C2 symmetric salen ligands (29a, b) with four C8Fi7 ponytails have been prepared (Scheme 5) and their Mn(II) complexes evaluated as chiral catalysts for the aerobic oxidation of alkenes under FBS-modified Mukaiyama conditions. Both complexes are active catalysts (isolated yields of epoxides up to 85%) under unusually low catalyst loadings (1.5% cf. the usual 12%). Although catalyst recovery and re-use was demonstrated, low enantioselectivities were observed in most cases. 

The synthesis of N phthaloyl enamides has been reported by a remarkably general method for aerobic oxidative amination of unactivated alkyl olefins as shown in Scheme 9.6 [12]. From a practical synthesis point of view, the phthalimide can not only serve as a directing group for asymmetric hydrogenation but can also be removed under mild conditions. 

Membrane proteins have a variety of functions. Most, but not all, of the important functions of the membrane as a whole are those of the protein component. Transport proteins help move substances in and out of the cell, and receptor proteins are important in the transfer of extracellular signals, such as those carried by hormones or neurotransmitters, into the cell. In addition, some enzymes are tightly bound to membranes examples include many of the enzymes responsible for aerobic oxidation reactions, which are found in specific parts of mitochondrial membranes. Some of these enzymes are on the inner surface of the membrane, and some are on the outer surface. There is an uneven distribution of proteins of all types on the inner and outer layers of all cell membranes, just as there is an asymmetric distribution of lipids. 

Asymmetric induction by polymer-immobilized complexes is an important reaction in oxidation processes (this has already been demonstrated for the hydrogenation transformations described in Section 12.2.9). There are three different methods of synthesis of optically active compounds from optically inactive racemic mixtures spontaneous, biochemical and chemical. The chemical method is the most common. Immobilized metal complexes are the best models of asymmetric induction by enzymes. They produce large quantities of enantiomeric products from small quantities of chiral compounds. (Ascorbate oxidase is a copper-containing enzyme catalyzing aerobic oxidation of vitamin C. Its... 

Furthermore, we observed asymmetric induction in the aerobic oxidation with the PYML-6-Fe(II) complex in the presence of reducing agent, i.e., cis- and frans-P-methylstyrenes were oxidized with PYML-6-Fe(II)-02-(2-mercapto-ethanol) system to give (— )-cis-epoxide (51% ee) and racemic trans-epoxide, respectively (Table 4) [62]. The major product of this reaction was benzalde-... 

Table 3.1 Asymmetric aerobic oxidative biaryl coupling reactions reported by Nakajima.

Scheme 3.4 Proposed mechanism for the asymmetric aerobic oxidative hiaryl coupling reactions.

Scheme 3.5 An overall catalytic cycle proposed for the asymmetric aerobic oxidative biaryl coupling catalyzed by chiral Cu-diamine complex.

Table 3.3 Asymmetric aerobic oxidative biatyl coupling reactions reported by Sekar.

In 2000, Katsuki and co-workers applied the chiral chloro nitrosyl Ru -(salen) complex developed in their own group to asymmetric aerobic oxidative biaryl coupling reactions (Scheme 3.14). The reaction was found to proceed smoothly in air under irradiation with a halogen lamp as the light source at room temperature. Examination of a series of Ru (salen) complexes revealed that the combination of (R,R)-diamine unit and (R)-BINOL scaffold in the catalyst is important for achieving higher enantioselectivity. The absolute configuration of the major product is determined by the chirality of the BINOL scaffold whereas the structural variation in the diamine part shows little influence on asymmetric induction. Under the optimal conditions, several 2-naphthols with a substituent at the C6 position of the naphthalene... 

Optically active a-substituted phenyloxyacyloxy and aryloxy phosphonates have been synthesized via catalytic asymmetric hydrogenation of the corresponding prochiral a,P-unsaturated phosphonates using Rh(i)/(7, i )-Me-DuPhos as the catalyst. The reactions exhibit excellent enantioselectivity with ee up to 96%. A new kinetic resolution process for a-hydroxyphosphonates with the assistance of N-salicylidene-L-tert-leucine-based vanadyl(v) methoxide complexes (209), achieving highly enantioselective and chemoselective aerobic oxidation at ambient temperature (Scheme 78). ... 

Heterogeneous catalysts such as Ru-Al-Mg-hydrotaldte, Ru-Co-Al-hydrotalcite, Ru-hydroxyapatite (RuHAP) (Eq. (7.40)) [91], RU-AI2O3 [92a,b], and Ru/A10(OH) [92c] are highly efficient catalysts for aerobic oxidation of alcohols. In these oxidation reactions, the key step is postulated as the reaction of Ru-H with O2 to form Ru-OO H, in analogy to Pd-OOH, which has been shown to operate in the palladium-catalyzed Wacker-type asymmetric oxidation reaction [93]. It is noteworthy that ruthenium on carbon is simple and efficient for the oxidation of alcohols (Eq. (7.41)) [92d]. 

Kinetic resolution of secondary alcohols and desymmetrization of diols were reported by asymmetric oxidation using chiral (nitrosyl)Ru(salen) chloride (31) (Eq. (7.42)) [97] in addition to the aerobic oxidation reaction [97d]. 

Egami, H. and Katsuki, T. (2009). Iron-Catalyzed Asymmetric Aerobic Oxidation oxidative CoupUng of 2-Naphthols, J. Am. Chem. Soc., 131, pp. 6082-6083. 

Scheme 18 Asymmetric aerobic oxidation/double [3-1-2] cycloaddition of azomethine ylides with cyclopentadiene...

The effect of amine ligands in copper(I)-catalyzed chemose-lective amide carbamoylation has been studied. Catalytic asymmetric synthesis of binaphthol derivatives is also reported by aerobic oxidative coupling of 3-hydroxy-2-naphthoates with chiral diamine-copper complexes (eq 15). ... 

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