Asymmetric reduction olefinic ketones

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... 

The enantioselective hydrogenation of olefins, ketones and imines still represents an important topic and various highly enantioselective processes based on chiral Rh, Ru or Ir complexes have been reported. However, most of these catalysts failed to give satisfactory results in the asymmetric hydrogenation of aromatic and heteroaromatic compounds and examples of efficient catalysts are rare. This is especially the case for the partial reduction of quinoline derivatives which provide 1,2,3,4-tetrahydroquinolines, important synthetic intermediates in the preparation of pharmaceutical and agrochemical products. Additionally, many alkaloid natural products consist of this stmctural key element. 

More successful asymmetric reductions have been based on amine (particularly alkaloid) complexes of bis(dimethylglyoximato) cobalt(II), also known as cobaloxime(II) and represented Co(dmg)2 (compound VII). Cobaloxime-chiral amine complexes have been used to catalyze the hydrogenation of both olefinic and ketonic substrates (Fig. 24). It has been determined that hydroxyamine modifiers, for example, alkaloids such as quinine, quinidine, and cinchonidine, are most effective. The highest optical purity obtained thus far has been 71%, observed for reduction of benzil in benzene solution at 10° using quinine as the... 

Two types of asymmetric reactions were conducted synthesis of styrene oxide and reduction of olefinic ketones. 

Precursor of Useful Chiral Ligands. OPEN is widely used for the preparation of chiral ligands. Organometallic compounds with these ligands act as useful reagents or catalysts in asymmetric induction reactions such as dihydroxylation of olefins, transfer hydrogenation of ketones and imines, Diels-Alder and aldol reactions, desymmetrization of meso-diols to produce chiral oxazolidinones, epoxidation of simple olefins, benzylic hydroxylation, and borohydride reduction of ketones, imines, and a,p-unsaturated carboxylates. ... 

During the last decade, use of oxazaborolidines and dioxaborolidines in enantioselective catalysis has gained importance. [1, 2] One of the earliest examples of oxazaborolidines as an enantioselective catalyst in the reduction of ketones/ketoxime ethers to secondary alco-hols/amines was reported by Itsuno et al. [3] in which (5 )-valinol was used as a chiral ligand. Since then, a number of other oxazaborolidines and dioxaborolidines have been investigated as enantioselective catalysts in a number of organic transformations viz a) reduction of ketones to alcohols, b) addition of dialkyl zinc to aldehydes, c) asymmetric allylation of aldehydes, d) Diels-Alder cycloaddition reactions, e) Mukaiyama Michael type of aldol condensations, f) cyclopropana-tion reaction of olefins. 

Metal alkoxides have promising role in catalytic reactions. In this chapter, we briefly review the history, chciracteristics, cuid synthesis routes of metal alkoxide and then discuss some catalytic processes that are performed with them. These processes include polymerization of different olefin oxides and cyclic esters asymmetric reduction of aldehydes and ketones oxidation of sulfides and olefins and a variety of other asymmetric reactions. The rest of the chapter discusses the characteristics of these catalytic systems from different points of view. 

Makino et al. (1977) and Baba et al. (1980e) reported the asymmetric reduction of a,3-unsaturated iminium salts that were produced from isophorone and secondary amines. Since the reduced product can be hydrolyzed to give a saturated ketone as shown in Scheme 15, reduction of this type is equivalent to the reduction of the olefinic double bond in an a,3-unsaturated ketone. Stereochemical results are listed in Table 6. It was found that the iminium salt which afforded the highest e.e. was the one that is derived from pyrrolidine. The e.e. value was independent of the kind of counter anion. 

Asymmetric catalytic reduction reactions represent one of the most efficient and convenient methods to prepare a wide range of enantiomerically pure compounds (i.e. a-amino acids can be prepared from a-enamides, alcohols from ketones and amines from oximes or imines). The chirality transfer can be accomplished by different types of chiral catalysts metallic catalysts are very efficient for the hydrogenation of olefins, some ketones and oximes, while nonmetallic catalysts provide a complementary method for ketone and oxime hydrogenation. 

REGIO- AND STEREO-CONTROLLED OXIDATIONS AND REDUCTIONS Table 6.7 Asymmetric epoxidation of olefins by ketone 2. 

The BINAL-H reagents exhibit exceptionally high enantioface-dif-ferentiating ability in the reduction of prochiral ketones that have unsaturated substituents such as aromatic rings, olefinic and acetylenic groups, etc. The general sense of asymmetric induction of simple car-... 

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