Ketones hydroxylation

Various biocatalytic options have been presented for the desymmetrization of meso-diols to chiral hydroxyl-ketones. A particularly facile system is represented by... 

When diketone 55 was reduced to hydroxyl ketone 56, an interesting change occurred in the H NMR that gave us significant insight into for our proposed conformations of these systems. A selected region of the H NMR for compounds 2 and 56 is shown in Fig. 8.9. 

Starting from ketone(i )-/(S )-49, the asymmetric aldol reaction with aldehyde in the presence of 45a or 45b affords all four isomers of //-hydroxyl ketone 47, 48, 50, and 51 with high yields and stereoselectivities (Scheme 3-17). 

TABLE 4-21. Asymmetric Oxidation of Prochiral Ketone Enolates to a-Hydroxyl Ketones Using 147... 

Following their success with chiral ketone-mediated asymmetric epoxidation of unfunctionalized olefins, Zhu et al.113 further extended this chemistry to prochiral enol silyl ethers or prochiral enol esters. As the resultant compounds can easily be converted to the corresponding a-hydroxyl ketones, this method may also be regarded as a kind of a-hydroxylation method for carbonyl substrates. Thus, as shown in Scheme 4-58, the asymmetric epoxidation of enol silyl... 

Allylation and subsequent protection of the thus formed hydroxyl group furnishes compound 134, which bears the C-ring skeleton of baccatin HI. Removal of the C-9 silyl group, PhLi treatment of the resulting hydroxyl ketone, and in situ acetylation provides compound 135, which has the C-2 benzoate functionality. In the presence of a guanidinium base, equilibrium between the C-9 to C-10 carbonyl-acetate functional groups can be established. Thus, the desired C-9-carbonyl-C-10-acetate moiety 136 can be separated from the mixture. Compound 136 is then converted to aldehyde 137 via ozonolysis for further construction of the C-ring system (Scheme 7-40). 

Titanium silicate molecular sieves not only catalyze the oxidation of C=C double bonds but can be successfully employed for the oxidative cleavage of carbon-nitrogen double bonds as well. Tosylhydrazones and imines are oxidized to their corresponding carbonyl compounds (243) (Scheme 19). Similarly, oximes can be cleaved to their corresponding carbonyl compounds (165). The conversion of cyclic dienes into hydroxyl ketones or lactones is a novel reaction reported by Kumar et al. (165) (Scheme 20). Thus, when cyclopentadienes, 1,3-cyclohexadiene, or furan is treated with aqueous H202 in acetone at reflux temperatures for 6 h in the presence of TS-1, the corresponding hydroxyl ketone or lactone is obtained in moderate to good yields (208). 

The basic structure of humic substances involves a backbone composed of alkyl or aromatic units crosslinked mainly by oxygen and nitrogen groups. Major functional groups attached to the backbone are carboxylic acids, phenolic hydroxyls, alcoholic hydroxyls, ketones, and quinones. The molecular structure is variable as it is dependent on the collection of DOM available in seawater to undergo the various polymerization, condensation, and oxidation reactions and reaction conditions involved in humification, as well as the ambient physicochemical reaction conditions, such as temperature and light availability. 

Dynamic Kinetic Resolutions (DKR) are documented in the chemical literature [17, 18], and it was envisaged that such a system was, in theory, possible with the aryl-substituted morpholinols 2. The morpholinol ring system may exist, in part, as the open chain hydroxyl ketone (see Scheme 10.1), and it has been reported [19,... 

Trost et al. [11] reported another impressive example of bimetallic catalysts in which a Zn-Zn homobimetallic complex (17, Scheme 7) serves as an effective catalyst for direct aldol reactions [11-13]. The proposed structure of the catalyst was verified by mass spectrometry and the best ratio of Et2Zn and the ligand. The chemical yield was moderate in the reaction of methyl ketones (1) (Scheme 7, top) [11,12], but a highly atom-economic system was achieved when a-hydroxylated ketones (10) were used as a substrate (Scheme 7, bottom) [13]. Excellent diastereo- and enantioselectivity were obtained under mild conditions. In contrast to the case of Shibasaki s heteropolymetallic catalyst, syn-1,2-diols (syn-11) were obtained as the major diastereomers. 

Carbohydrates are characterized by the presence of polyhydroxylic aldehyde or poly-hydroxylic ketone structures or polymers of such units. Sugars and polysaccharides have definite three-dimensional structures that are important for many biological functions. They are hydrophilic and thus easily accessible to aqueous reaction mediums. The chemistry of bioconjugation using carbohydrate molecules begins with an understanding of the building blocks of polysaccharide molecules. 

Hydroxyl ketones, asymmetric hydrogenation, 10, 47 Hydroxyl-substituted cyclopropanes, solvomercuration,... 

Enantioselective a-hydroxylation of carbonyl compounds,2 Useful enantiose-lectivity (60-95% ee) obtains in the oxidation of enolates of a number of carbonyl compounds (ketones, esters, amides) with the simplest member of this series, ( + )-or (— )-l. This reagent, however, is not useful for enantioselective oxidations resulting in tertiary a-hydroxyl ketones. For this purpose, the 8,8-dichloro derivative (2) of ( + )-l is markedly superior, as shown in equation (I). This derivative can also be... 

A series of pyrrolidines was conveniently prepared in a microwave-assisted double alkylation of aniline derivatives with alkyl dihalides in water in the presence of K2CO3 as a base (Scheme 1) [12,13]. Although the reaction mixture could be regarded as a multi-phase system, as neither reactant was soluble in the mildly basic aqueous medium, the microwave-assisted reaction proceeded readily without the use of phase-transfer reagents. The amount of side-reactions such as hydrolysis of bromides to alcohols in an alkaline reaction medium was substantially suppressed compared to the conventional thermal conditions. The reaction conditions were sufficiently mild to tolerate a variety of functional groups in anilines such as hydroxyls, ketones and esters. Alkyl bromides and tosylates were equally efficient as alkylating agents. Notably, isolation and purification comprised simply of phase separations (filtration or decantation) of the desired product from the aqueous media. 

Transmetallation between stannyl esters and SnCl2 affords tin(ll) enolate equivalents. The reaction of cr-stannyl esters with a-alkoxy or hydroxyl ketones in the presence of SnCl2 gives aldol-type products with high selectivities in a chlelation-controlled manner (Equation (88)).245... 

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