Enantioselective oxidations applications

Mejorado, L. H. Pettus, T. R. R. Total synthesis of (+ )-rishirilide B development and application of general processes for enantioselective oxidative dearomatization of resorcinol derivatives. J. Am. Chem. Soc. 2006, 128, 15625-15631. 

The most common oxidation states and the corresponding electronic configurations of osmium are +2 (d) and + (d), which are usually octahedral. Stable oxidation states that have various coordination geometries include —2 (dC)), and 0 (d), to +8 (d). The single most important application is Os04 oxidation of olefins to diols. Enantioselective oxidations have also been demonstrated. 

KiljunenE, KanervaLT (1999) Novel Applications of Chloroperoxidase Enantioselective Oxidation of Racemic Epoxyalcohols. Tetrahedron Asym 10 3529... 

Later, these studies were developed in work [64, 65] in which Pt(II) diphosphine complex was used as the catalyst of oxidation with hydrogen peroxide. Modifications of the catalytic system mentioned were applied to enantioselective oxidation [66], However, these catalytic systems find limited application, because they are active in transformations of cyclic ketones only [67],... 

Kiljunen E, Kanerva LT (1999) Novel applications of chloroperoxidase enantioselective oxidation of racemic epoxyalcohols. Tetrahedron Asymm 10 3529-3535... 

Compared to reductions the oxidation reactions constitute an area that is still relatively unexplored from a large-scale point of view. In spite of the enormous efforts which have been spent on basic research, applications at scale are still scarce. The reasons for this could be that the asymmetric procedures currently at hand are deemed to be inefficient, that the types of functional group interconversions addressed with oxidations are far less in demand than is the case for reductions, or the existence of competitive stoichiometric methods (mostly based on the use of metal oxides and salts, such as fTO, and KM 1104) that are considered to be sufficient for most purposes. Another factor that needs to be included is the intrinsic difficulty in designing a catalyst that is stable under the relatively aggressive oxidative conditions (compare reactivity of [H] and [O]). Nonetheless, the capabihty of enantioselective oxidations has been unambiguously proven at the manufacturing level in enough cases to make this approach a viable option for commercial production (see Sections 2.2 and 2.3). 

The enantioselective oxidation of amphetamine SS by copper containing amine oxidases from Escherichia coli and Klebsiella oxytoca was reported in 2000 by Had salihoglu et al. [34] Moderate E values of 1S were obtained, opening up the possibility for future applications of amine oxidase catalyzed resolutions of substi tuted amphetamines (Figure 14.2S). 

Kinetic resolution." In the resolution of 1-aryl- and 1-heteroarylethanols by enantioselective oxidation the ee value of the (5)-isomer reaches 86-100% when the ethanol has either a phenyl, 2-furyl, or 2-thienyl group. The value of the 2-pyridyl derivative is lower (40% ee). The method is not applicable to l-(2-thiazolyl)ethanol... 

Hypervalent iodine reagents are commonly used for the oxidation of organosulfiir compounds. Applications of hypervalent iodine reagents for the preparation of sulfoxides, including enantioselective oxidations of organic sulfides, have been summarized in reviews [519,520]. 

The first reported examples concern the oxidation of NADH catalyzed by the NOX from L. brevis and I. sanfranciscensis [53, 64], which were coupled to the enantioselective oxidation of DL-leucine catalyzed by t-leudne dehydrogenase and to the oxidation of L-glutamate to a-ketoglutarate catalyzed by L-glutamate dehydrogenase, respectively. Unfortunately, these two NOXs showed a low suitabihty for a wider application on preparative scale because of product inhibition and a Hmited stability under operative conditions [1, 64, 65]. 

Turner s group demonstrated that a variety of 3,4-substituted mcso-pyrrolidines can be enantioselectively oxidized by the monoamine oxidase (MAO) mutant. The -p3UToline products were converted to amino acids through the corresponding nitriles. In another application, the chiral A -pyrrolines were directly used to prepare prolyl peptides in an Ugj reaction. This reaction has been applied to an efficient synthesis of Telaprevir. The directed evolution of MAO from Aspergillus niger provided variant with a broadened substrate specificity and high enanhoselectivity for several a-methyl amines. In further enzyme evolution, an improved variant was identified for secondary amines [165,166]. 

Asymmetric synthesis of amines is a synthetically important research area due to the broad range of applications of chiral amines in fhe field of pharmaceuticals [134]. Amine oxidases are a versatile class of catalysts, which turned out to be very suitable for the preparation of chiral amines by means of desymmetrization or deracemization reactions. With respect to the latter, a racemic amine is enantioselectively oxidized by the amine oxidase, and simultaneously the in situ-formed imines or iminium ions, respectively, are reduced in a nonenantioselective chemical reduction process (with typically a borohydride) back to the racemic amine [135]. The key catalyst for such a... 

The application of this biphasic system to the asymmetric oxidation of arylmethylsulfides [9] did not lead to such successful results. Conversions (78-100%) and selectivities to sulfoxide (88-99%) were excellent, much better in general than in homogeneous phase, but enantioselectivities were always very low (up to 17% ee). 

Application of these ligands to the hydroboration-oxidation of styrene proceeded with moderate yields and much lower enantioselectivities than for norbornene. The best result was with (R, R)-38, which afforded (A)-l-phenyletha-nol in 61% yield and 42% ee. However, Bianchini s (R, 7 )-BDPBzP 39 was even less efficient for this substrate, and gave both poor yields (29%) and poor enantioselectivities (26% ee) for the hydroboration of styrene at 0°C.84... 

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