Optically active phenolic ketones

In a number of cases, however, enzymatic reactions do not take place specifically with respect to either enantiomer. One example of this is the demethylation of the methyl ether of racemic 8-aza-D-homoestradiol (291), which forms the racemic free phenol (292) [120] (Scheme 42). Another example is the racemic 18-norsteroid (294). Only the natural enantiomer of this compound reacts with an enzyme isolated from the bacterium Pseudomonas testosteroni, 3)3,17i3-hydroxysteroid dehydrogenase, forming the optically active 17-ketone (293). At the same time, both enantiomers of compound (294) react with another enzyme from the same source,... 

Chiral Ligand of L1A1H4 for the Enantioselective Reduction of Alkyl Phenyl Ketones. Optically active alcohols are important synthetic intermediates. There are two major chemical methods for synthesizing optically active alcohols from carbonyl compounds. One is asymmetric (enantioselective) reduction of ketones. The other is asymmetric (enantioselective) alkylation of aldehydes. Extensive attempts have been reported to modify Lithium Aluminum Hydride with chiral ligands in order to achieve enantioselective reduction of ketones. However, most of the chiral ligands used for the modification of LiAlHq are unidentate or bidentate, such as alcohol, phenol, amino alcohol, or amine derivatives. 

Direct separation of enantiomers may be performed on cellulose the use of microcrystalline cellulose is especially widely used. An other stationary phase is the microcrystalline triacetylcellulose, which is stable when using alcoholic and phenolic mobile phases however, it is unstable when glacial acetic acid and ketones are used. Optically active poly(meth)acrylate may be bound to the silica gel. and these stationary phases are widely used under the names of CHIRALPLATE or CHIR . Beta cyclodextrin can also be covalently bound to silica, and also reversed-phase plates may be used for chiral separation when the mobile phase consists of beta-cyclodextrin. 

A single enzyme is sometimes capable of many various oxidations. In the presence of NADH (reduced nicotinamide adenine dinucleotide), cyclohexanone oxygenase from Acinetobacter NCIB9871 converts aldehydes into acids, formates of alcohols, and alcohols ketones into esters (Baeyer-Villiger reaction), phenylboronic acids into phenols sulfides into optically active sulfoxides and selenides into selenoxides [1034], Horse liver alcohol dehydrogenase oxidizes primary alcohols to acids (esters) [1035] and secondary alcohols to ketones [1036]. Horseradish peroxidase accomplishes the dehydrogenative coupling [1037] and oxidation of phenols to quinones [1038]. Mushroom polyphenol oxidase hydroxylates phenols and oxidizes them to quinones [1039]. 

The 2-sulfonyloxaziridine (57) is a more selective oxidant than peracids. The reagent has been employed in the oxidation of sulfides to sulfoxides, disulfides to thiolsulfinates, selenides to selenoxides, thiols to sulfenic acids, organometallic reagents to alcohols and phenols, ketone and ester enolates to a-hydroxycarbonyl compounds (equation 31)41. The oxidation of chiral amide enolates gives optically active a-hydroxy carboxylic acids with 93-99% enantiomeric excess42. 

The nature of the achiral R OH affects chiral selectivity, and by using 3,5-dimethyl-phenol high optical yields of optically active secondary alcohols are obtained from ketones. A similar principle is seen in the alkylative conversion of aldehydes and ketones to alcohols by alkyl transfer from the aluminate (19), and in the reduction of ketones by a-aminoester boranes (20) in the presence of Lewis acids. 

Monoterpenes (Cio) are the simplest members of the terpene series. They result from the condensation of two isoprene units and may be acyclic, monocyclic, bicyclic or tricyclic. The monoterpenes can have another functional moiety like alcohol (geraniol, linalool, menthol, bomeol), aldehyde (geranial, cihonellal), ketone (menthone, carvone, thujone), ester (bomyl acetate, linalyl acetate), ether (1,8-cineol) and phenol (thymol, carvacol). In the case of optically active molecules, the proportions of the enantiomers vary largely from one species to another. 

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