Catalytic enantioselective reaction

Kobayashi S. Catalytic enantioselective reactions of aldimines nsing chiral Lewis acids in Curr. Trends Org. Synth., [Proc. Int. Conf. ], 12th. 1999 183-190, Eds. Scolastico C., Nicotra F., Pb. Acad. Plenum Pub. N.Y. 

Acetylenic esters react with arylboron reagents in the presence of rhodium diphosphine catalyst to give cyclic ketones.409 Equation (61) shows an example which may involve ortfe-metallation and ketone formation. A catalytic, enantioselective reaction was also achieved (Equation (62)). These processes presumably involve unprecedented addition of organorhodium species to the ester carbonyl group. 

In 1993, we reported that various unsaturated heterocycles can be alkylated with Et-, wPr- and nBuMgCl in the presence of optically pure (EBTHI)ZrCl2 (3a) or (EBTHI)Zr-binol (3b) to afford the derived unsaturated products in >90% ee (cf. 5 6, Scheme 2) [4a]. Many of the simpler five- and six-membered starting materials are available commercially or can be prepared by established procedures. In contrast, catalytic enantioselective reactions involving unsaturated medium ring hetero cycles were not a trivial undertaking the synthesis of these olefinic substrates, by the extant methods, was prohibitively cumbersome. 

Hoveyda in his essay on asymmetric catalysis in target-oriented synthesis (p 145). The concept of catalysis-based total synthesis, in which a series of catalytic enantioselective reactions are employed in combination with other catalytic reactions, is emerging as the desirable way to make complex natural products and medidnally-important target compounds. 

In other cases, such transformations are employed to construct the main skeleton of the target molecule. In yet another type of total synthesis, referred to as catalysis-based total syntheses, various catalytic enantioselective reactions are employed in combination with a number of other catalytic transformations. 

Enantioselective -Functionalization of Aldehydes and Ketones The direct and enantiosective functionalization of enolates or enolate equivalents with carbon-, nitrogen-, oxygen-, sulfur- or halogen-centered electrophiles represents a powerful transformation of chemical synthesis and of fundamental importance to modem practitioners of asymmetric molecule constmction. Independent studies from List, J0rgensen, Cordova, Hayashi, and MacMiUan have demonstrated the power of enamine catalysis, developing catalytic enantioselective reactions such as... 

Abstract The reversible reaction of primary or secondary amines with enolizable aldehydes or ketones affords nncleophilic intermediates, enamines. With chiral amines, catalytic enantioselective reactions via enamine intermediates become possible. In this review, structure-activity relationships and the scope as well as cnrrent limitations of enamine catalysis are discnssed. 

The application of a rhodium(I) catalyst bearing tunable bidentate phosphine ligands, such as 10, opened the possibility for the development of a new catalytic enantioselective reaction [13c]. In a control experiment, it was noted that the reaction with a catalyst containing a bidentate phosphine ligand, specifically RhCl(CO)(dppe), was significantly decelerated as compared to the reaction with [RhCl(CO)2]2 (Scheme 11.12). 

Amino Alcohol Catalyzed Alkylation. (—)-3-exo-(Dimethylamino)-isobomeol [( —)-DAIB] is a sterically restrained jS-dialkylamino alcohol that has proven to be an extremely efficient catalyst 13). For instance, in the presence of 2 mol % of (—)-DAIB, the reaction of benzaldehyde and diethylzinc proceeds smoothly to give, after aqueous workup, (5)-1 -phenyl-1 -propanol in 98% ee and in 97% yield along with a small amount of benzyl alcohol (Scheme 9). Nonpolar solvents such as toluene, hexane, ether, or their mixtures produce satisfactory results. The optical yield in toluene is affected by temperature and decreases from 98% at —20°C to less than 95% at 50°C. The catalytic enantioselective reaction has been extended to a range of alkylating agents and aldehyde substrates, which are summarized in Scheme 10 (75). p-Substituted ben-... 

Aires-de-Sousa, J. and Gasteiger, J. (2005) Prediction of enantiomeric excess in a combinatorial library of catalytic enantioselective reactions. /. Comb. Chem., 7, 298. 

Palladium enolate chemistry has been exploited to perform a range of catalytic enantioselective reactions on carbonyl substrates, including aldol, Michael, Mannich-type, and a-fluorination.154... 

Grubbs and co-workers have recently reported a new class of Ru catalysts (83, Eq 2) [29] that bear a chiral monodentate N-heterocyclic carbene ligand [30]. The reactions illustrated in Eq 2 include the highest ee reported (13-90% ee) asymmetric induction is clearly dependent on the degree of olefin substitution (cf. Schemes 18 and 4 for comparison with the Mo-catalyzed reactions of the same substrates). As is the case with nearly catalytic enantioselective reactions [4], the identity of the optimal catalyst depends on the substrate a number of chiral... 

The most intriguing work in the field of asymmetric oxidative aryl coupling has been directed towards finding catalytic enantioselective reactions. The main goal in these studies has been the synthesis of chiral binaphthyl units as an improvement over stoichiometric chiral reagent enantioselective syntheses. 

Bauer A, Westkamper F, Grimme S, Bach T (2005) Catalytic enantioselective reactions driven by photoinduced electron transfer. Nature 436 1139-1140... 

Development of the first spiro /v. v(isoxazoline) ligands and their applications to catalytic enantioselective reactions 04YGK59. 

Nitrogen-Containing Ligands Anchored onto Polymers as Catalyst Stabilizer for Catalytic Enantioselective Reactions... 

Titanium is one of the most important transition metals used in catalytic enantioselective reactions. Whereas rhodium, palladium, copper and ruthenium are rather rare in Nature, and the depletion of natural resources is evoked for these, titanium does not suffer from lack of availability. In fact, it is the 9th most abundant element on Earth and one of the cheapest transition metals. The products resulting from the hydrolysis of titanium complexes are nontoxic and do not cause any environmental problems. This low toxicity has allowed titanium to be used for multiple applications, including medical uses (prostheses, sun screens, etc.). 

The remaining chapters of this text describe catalytic reactions. Each of these catalytic reactions comprises stoichiometric reactions that have been presented so far in this text. Catalytic reactions are distinct from the stoichiometric reactions because the metal complexes in catalytic reactions are present in substoichiometric amounts. Chapter 14 presents some of the principles that apply to catalytic reactions, including enantioselective catalytic reactions. The content of this chapter applies to all reactions contained in the subsequent chapters of this text, as well as to catalytic reactions that lie outside of the scope of this text. Hre latter sections of Chapter 14 present principles that are specific to enantioselective catalysis. Catalytic enantioselective reactions form non-racemic, chiral products by virtue of the chirality of the catalyst. 

Cho, B.T. and Chun, Y.S., Catalytic enantioselective reactions. Part 12. Enantioselective addition of diethylzinc to aldehydes catalyzed by zinc complexes modified with chiral P-sulfonamido alcohols. Synthetic Commun., 29, 521,1999. 

In this chapter, we focus on acid catalysis in water. While there are numerous examples of catalytic reactions in water, the main body of these involves acid catalysis. Homogeneous catalysis, heterogeneous catalysis, and micellar catalysis, including catalytic enantioselective reactions, are discussed in detail. Acid-catalyzed reactions using a small amount of water may not be included unless they are crucial for the further development of the field. 

Inspired by Tepe s report of silver(I)acetate-catalyzed 1,3-DC reactions of miinchnone/alkene [56], in 2007, Toste and coworkers developed the first catalytic enantioselective reaction of azlactones 154 with alkenes 155 to provide A -pyrrolines 156 (Scheme 2.40). By using (S)-Cy-SEGPHOS(AuOBz)2 157 as the catalyst, the exo isomer was generated with generally high enantioselectivity [57]. The reaction... 

In 2010, a cooperative dual-catalyst system was reported to promote the highly enantioselective fluoride ring opening of various meso epoxides having alkene, ester, and protected amine functionalities. The reactions were conducted with a chiral (Salen)cobalt complex, (-)-tetramisole, benzoyl fluoride as a latent source of fluoride in the presence of HFIP. The efficient catalytic enantioselective reaction is explained by the generation of a (Salen)Co(III) fluoride under the cocatalytic conditions that occurred in good yields with up to 95% ee (Scheme 44.32). Racemic terminal epoxides, such as styrene oxide, were also studied, but they almost exclusively lead to the fluorine in the primary position therefore, the fluorine atom was not introduced on a stereogenic center. 

Enantiomeric Excess in a Combinatorial Library of Catalytic Enantioselective Reactions. 

On using enamine activation, nucleophiles were limited to aldehydes and ketones but the emergence of H-bonding activation [31] has expanded considerably this scope. With this mode of activation other carbon-centered nucleophiles and also heteroatom-centered nucleophiles could be considered. During the period 2003-2012, growing interest was focused on the ability to perform catalytic enantioselective reactions with small organic molecules able to produce such weak interactions. 

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