Meerwein-Ponndorf-Verley reduction asymmetric

Node, M., Nishide, K., Shigeta, Y., Shiraki, H., Obata, K. A Novel Tandem Michael Addition/Meerwein-Ponndorf-Verley Reduction Asymmetric Reduction of Acyclic a,P-Unsaturated Ketones Using A Chiral Mercapto Alcohol. J. Am. Chem. Soc. 2000, 122,1927-1936. 

As shown in Figure 1.26, a chiral Sm(III) complex catalyzes asymmetric reduction of aromatic ketones in 2-propanol with high enantioselectivity. Unlike other late-transition-metal catalysis, the hydrogen at C2 of 2-propanol directly migrates onto the carbonyl carbon of substrate via a six-membered transition state 26A, as seen in the Meerwein-Ponndorf-Verley reduction. ... 

Doering, W. von E., and R. W. Young Partially asymmetric Meerwein-Ponndorf-Verley reductions. J. Amer. chem. Soc. 72, 631 (1950). 

Nishide, K. and Node, M. (2002) Recent development of asymmetric syntheses based on the Meerwein-Ponndorf-Verley reduction. Chirality, 14, 759—767. 

Yu and coworkers reported that use of PrSBEt2 as an additive accelerates the chiral Zr-catalyzed asymmetric allylation reaction and suppresses the concomitant Meerwein-Ponndorf-Verley reduction. The presence of the additive is thought to dissociate the product from the reaction complex and to regenerate the chiral catalyst [28]. This method was further extended to asymmetric propargylation with allenyltributylstannane by the same group [19]. In contrast, Taghavini and Umani-Ronchi and their group have shown that an enantioselective allylation of... 

Meerwein-Ponndorf-Verley reduction. The samarium iodide is a catalyst tor asymmetric reduction (36-96% yield, up to 97% ee) of carbonyl compounds by / PrOH. 

Perhaps the simplest case of asymmetric synthesis to visualize is a reaction between an achiral molecule and a chiral reagent in such a way that a new chiral center is created at the reaction site. One such reaction is the Meerwein-Ponndorf-Verley reduction of ketones with aluminum salts of optically active alcohols. The... 

Meerwein-Ponndorf-Verley reductions, unlike many asymmetric reductions, involve a reversible redox reaction. Hydride transfer from the asymmetric center is believed to take place within a six-membered cyclic transition state (A) or (B), Fig. 9]. The lower-energy transition state will be that having the larger groups trans [(B) in Fig. 9]. The enantiomer of the product carbinol which results from this lower-energy transition state will predominate in a kinetically controlled, asymmetric Meerwein-Ponndorf-Verley reduction. 

Meerwein-Ponndorf-Verley type asymmetric reduction has also been accomplished with alkyloxy magnesium halides prepared from optically active alcohols. Optically active 2-octyloxy-2-d magnesium bromide reduced butyraldehyde to optically active n-butyl-1-d alcohol (Streitwieser, 1953). Reduction of benzaldehyde with 1-deuteroisobornyloxy magnesium halide produced optically active benzyl-l-d alcohol (Streitwieser and Wolfe, 1957 Streitwieser et al, 1959). 

Catalytic Asymmetric Meerwein-Ponndorf-Verley Reduction of Ketones... 

Scheme 13.38 Catalytic asymmetric Meerwein-Ponndorf-Verley reduction.

Recent reviews on asymmetric Meerwein-Ponndorf-Verley reductions, see (a) Cha, ).S. (2006) Organic Process Research and Development, 10, 1032. (b) Nishide, K., Node, M. (2002) Chirality, 14, 759. The reaction with lanthanide metals was established by Kagan, see (c) Namy, J.L., Souppe, )., Collin,... 

Fig. 8.36. As the asymmetric center of citronellal is unaffected by the reactions, all of the isopulegol and menthol isomers formed have the correct stereochemistry at Cl of the /i-menthane skeleton. There are therefore two strategies for recycling unwanted isomers. The first is to purify the ( )-isopulegol (172) by crystallization and recycle (178-180) back to citronellal by pyrolysis [221, 223, 224]. The second is to hydrogenate the mixture, separate the (—)-menthol by crystallization and treat the remainder with aluminium isopropoxide, which converts all of them, by Oppenauer oxidation, enoliza-tion, reketonization and Meerwein-Ponndorf-Verley reduction, to (—)-menthol, which is the thermodynamically most stable isomer (225).

In the fourth and final chapter, Howard Haubenstock discusses asymmetric reduction of organic molecules. Within this general topic of wide and continuing interest, Haubenstock s chapter deals with chiral derivatives of lithium aluminum hydride, their preparation from suitable amino or hydroxy compounds, and their use in reducing carbonyl groups. Related reactions of the Meerwein-Ponndorf-Verley type or involving tri-alkylaluminum reagents are also presented. 

Figure 1.26. Asymmetric Meerwein-Ponndorf-Verley-type reduction of ketones catalyzed by a Sm complex.

A tandem 1,4-addition-Meerwein-Ponndorf-Verley (MPV) reduction allows the reduction of a, /i-unsaturated ketones with excellent ee and in good yield using a camphor-based thiol as reductant.274 The 1,4-addition is reversible and the high ee stems from the subsequent 1,7-hydride shift the overall process is thus one of dynamic kinetic resolution. A crossover experiment demonstrated that the shift is intramolecular. Subsequent reductive desulfurization yielded fiilly saturated compounds in an impressive overall asymmetric reductive technique with apparently wide general applicability. 

The use of Al(III) complexes as catalysts in Lewis acid mediated reactions has been known for years. However, recent years have witnessed interesting developments in this area with the use of ingeiuously designed neutral tri-coordinate Al(lll) chelates. Representative examples involving such chelates as catalysts include (1) asymmetric acyl halide-aldehyde cyclocondensations, " (2) asymmetric Meerwein-Schmidt-Ponndorf-Verley reduction of prochiral ketones, (3) aldol transfer reactions and (4) asymmetric rearrangement of a-amino aldehydes to access optically active a-hydroxy ketones. It is important to point out that, in most cases, the use of a chelating ligand appears critical for effective catalytic activity and enantioselectivity. 

Tagliavini and Umani-Ronchi found that chiral BINOL-Zr complex 9 as well as the BINOL-Ti complexes can catalyze the asymmetric allylation of aldehydes with allylic stannanes (Scheme 9) [27]. The chiral Zr catalyst 9 is prepared from (S)-BINOL and commercially available Zr(0 Pr)4 Pr0H. The reaction rate of the catalytic system is high in comparison with that of the BINOL-Ti catalyst 4, however, the Zr-catalyzed allylation reaction is sometimes accompanied by an undesired Meerwein-Ponndorf-Verley type reduction of aldehydes. The Zr complex 9 is appropriate for aromatic aldehydes to obtain high enantiomeric excess, while the Ti complex 4 is favored for aUphatic aldehydes. A chiral amplification phenomenon has, to a small extent, been observed for the chiral Zr complex-catalyzed allylation reaction of benzaldehyde. 

The asymmetric reduction of prochiral ketones to their corresponding enantiomerically enriched alcohols is one of the most important molecular transformations in synthetic chemistry (20,21). The products are versatile intermediates for the synthesis of pharmaceuticals, biologically active compounds and fine chemicals (22,23). The racemic reversible reduction of carbonyls to carbinols with superstoichiometric amounts of aluminium alkoxides in alcohols was independently discovered by Meerwein, Ponndorf and Verley (MPV) in 1925 (21—26). Only in the early 1990s, first successful versions of catalytic... 

The development of aluminium-based catalysts for the asymmetric Meerwein-Schmidt-Ponndorf-Verley-Oppenauer (MSPVO) reduction/oxidation systems is reviewed with emphasis on the mechanistic understanding of the origin for activity and selectivity in monometallic catalysts.252... 

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