Ketones catalytic asymmetric

Scheme 8. Catalytic asymmetric Diels-Alder approach to ketone 30.

The past thirty years have witnessed great advances in the selective synthesis of epoxides, and numerous regio-, chemo-, enantio-, and diastereoselective methods have been developed. Discovered in 1980, the Katsuki-Sharpless catalytic asymmetric epoxidation of allylic alcohols, in which a catalyst for the first time demonstrated both high selectivity and substrate promiscuity, was the first practical entry into the world of chiral 2,3-epoxy alcohols [10, 11]. Asymmetric catalysis of the epoxidation of unfunctionalized olefins through the use of Jacobsen s chiral [(sale-i i) Mi iln] [12] or Shi s chiral ketones [13] as oxidants is also well established. Catalytic asymmetric epoxidations have been comprehensively reviewed [14, 15]. 

Shibasaki et al. also developed catalytic reactions of copper, some of which can be applied to catalytic asymmetric reactions. Catalytic aldol reactions of silicon enolates to ketones proceed using catalytic amounts of CuF (2.5 mol%) and a stoichiometric amount of (EtO)3SiF (120 mol%) (Scheme 104).500 Enantioselective alkenylation catalyzed by a complex derived from CuF and a chiral diphosphine ligand 237 is shown in Scheme 105.501 Catalytic cyanomethyla-tion by using TMSCH2CN was also reported, as shown in Scheme 106.502... 

The mechanism of the Meerwein-Pondorf-Verley reaction is by coordination of a Lewis acid to isopropanol and the substrate ketone, followed by intermolecular hydride transfer, by beta elimination [41]. Initially, the mechanism of catalytic asymmetric transfer hydrogenation was thought to follow a similar course. Indeed, Backvall et al. have proposed this with the Shvo catalyst [42], though Casey et al. found evidence for a non-metal-activation of the carbonyl (i.e., concerted proton and hydride transfer [43]). This follows a similar mechanism to that proposed by Noyori [44] and Andersson [45], for the ruthenium arene-based catalysts. By the use of deuterium-labeling studies, Backvall has shown that different catalysts seem to be involved in different reaction mechanisms [46]. 

CATALYTIC ASYMMETRIC ADDITIONS OF DIALKYLZINC TO KETONES ENANTIOSELECTIVE FORMATION OF TERTIARY ALCOHOLS... 

S.3.2 A C2 Symmetric Chiral Ketone for Catalytic Asymmetric Epox-idation of Unfunctionalized Olefins. Yang et al.105 reported the use of... 

Preparation of enantiomerically pare secondary amines by catalytic asymmetric hydrogenation or hydrosilylation of imines is as important as the preparation of alcohols from ketones. However, asymmetric hydrogenation of prochiral ON double bonds has received relatively less attention despite the obvious preparative potential of this process.98... 

Besides the above-mentioned catalytic asymmetric hydrogenation method for preparing fluorine-containing compounds, other reactions such as asymmetric reduction of achiral fluorine-containing ketones are also feasible methods for preparing chiral fluorinated compounds. For example, the oxazabor-olidine system, which has been discussed in Chapter 6, can also be employed in the catalytic reduction of trifluoromethyl ketones. Scheme 8 40 depicts some examples.85... 

Abstract In the first part of this mini review a variety of efficient asymmetric catalysis using heterobime-tallic complexes is discussed. Since these complexes function at the same time as both a Lewis acid and a Bronsted base, similar to enzymes, they make possible many catalytic asymmetric reactions such as nitroal-dol, aldol, Michael, Michael-aldol, hydrophosphonyla-tion, hydrophosphination, protonation, epoxide opening, Diels-Alder and epoxi-dation reaction of a, 3-unsaturated ketones. In the second part catalytic asymmetric reactions such as cya-nosilylations of aldehydes... 

Y. M. A Yamada, N. Yoshikawa, H. Sasai, M. Shibasaki, Direct Catalytic Asymmetric Aldol Reactions of Aldehydes and Unmodified Ketones, Angew. Chem. Int. Ed EngL 1997, 36,1871-1873. 

Asymmetric reduction of ketones or aldehydes to chiral alcohols has received considerable attention. Methods to accomplish this include catalytic asymmetric hydrogenation, hydrosilylation, enzymatic reduction, reductions with biomimetic model systems, and chirally modified metal hydride and alkyl metal reagents. This chapter will be concerned with chiral aluminum-containing reducing re-... 

Catalytic asymmetric methylation of 6,7-dichloro-5-methoxy-2-phenyl-l-indanone with methyl chloride in 50% sodium hydroxide/toluene using M-(p-trifluoro-methylbenzyDcinchoninium bromide as chiral phase transfer catalyst produces (S)-(+)-6,7-dichloro-5-methoxy-2-methyl-2--phenyl-l-indanone in 94% ee and 95% yield. Under similar conditions, via an asymmetric modification of the Robinson annulation enqploying 1,3-dichloro-2-butene (Wichterle reagent) as a methyl vinyl ketone surrogate, 6,7 dichloro-5-methoxy 2-propyl-l-indanone is alkylated to (S)-(+)-6,7-dichloro-2-(3-chloro-2-butenyl)-2,3 dihydroxy-5-methoxy-2-propyl-l-inden-l-one in 92% ee and 99% yield. Kinetic and mechanistic studies provide evidence for an intermediate dimeric catalyst species and subsequent formation of a tight ion pair between catalyst and substrate. 

Catalytic asymmetric reduction of unsaturated compounds is one of the most reliable methods used to synthsize the corresponding chiral saturated products. Chiral transition metal complexes repeatedly activate an organic or inorganic hydride source, and transfer the hydride to olefins, ketones, or imines from one... 

Modifications to the architecture of the imidazolidinone catalyst provided the fnryl derivative (20) which proved to be a powerfnl catalyst for the catalytic asymmetric Diels-Alder cycloaddition of simple a,P-unsaturated ketones [50]. Although... 

Scheme 60 Catalytic asymmetric formation of epoxides from a,p-unsaturated ketones...

In conjunction with the chiral anion TRIP (156) (10 mol%), diamine 157 (10 mol%) can be used in the catalytic asymmetric epoxidation of a,p-unsaturated ketones (>90% ee) [196], while the secondary amine 158 (10 mol%) can be used for the epoxidation of both di- and trisubstituted a,P-unsaturated aldehydes (92-98% ee) (Fig. 15) [211], The facile nature of these reactions, using commercially available peroxides as the stoichiometric oxidant, together with the synthetic utility of the epoxide products suggests application in target oriented synthesis. 

The paramount significance of chiral amines in pharmaceutical and agrochemical substances drives the development of efficient catalytic asymmetric methods for their formation. In contrast to the high enantioselectivities observed in asymmetric reduction of both alkenes and ketones, only limited success has been achieved in the enantiose-lective hydrogenation of imines [118]. Currently, there are few efficient chiral catalytic systems available for the asymmetric hydrogenation of imines. 

The catalytic asymmetric diboration of allenes provides a-substituted 2-boronyl allylic boronates of type 25 (see Eq. 32). One of them, 91, adds to ben-zaldehyde, albeit with a slight erosion of stereoselectivity (Eq. 65). The major P-hydroxy ketone stereoisomer, isolated after an oxidative work-up, originates from the putative chairlike transition structure 92. 

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