Hydroxylation asymmetric

Diastereoselective hydroxylation of enolates of chiral amides. Davis and coworkers1 have examined the asymmetric hydroxylation of the tetrasubstituted enolates of a chiral amide (2) with these chiral camphoryloxaziridines. Oxidation of the lithium enolate of 2 with (+ )-l proceeds with only moderate diastereoselectivity (48.4% de), which is somewhat less than that observed on hydroxylation with the achiral 2-(phenylsulfonyl)-3-phenyloxaziridine (4). Oxidation of the enolate of 2... 

Figure 4.17 The trioses D-glyceraldehyde (aldose) and dihydroxyacetone (ketose), the pentose D-ribose, the hexoses D-galactose and D-glucose (aldoses) and the ketohexose D-fructose in their open chain forms. The configuration of the asymmetrical hydroxyl group on the carbon, the furthest away from the aldehyde or ketone group, determines the assignment of D- or L-configuration.

Asymmetric hydroxylation of alkenes with osmium tetroxide... 

The (S,S)-enantiomer of 62, but not 62 itself, is available from cinnamaldehyde via an asymmetric hydroxylation reaction involving fermenting Baker s yeast Fronza, G. Fuganti, C. Grasselli, P. J. Chem. Soc., Chem. Commun. 1980, 442. 

An organocatalytic asymmetric hydroxylation was developed using spiro-Meldrum s acid derivatives, 20mol% proline, and nitrosobenzene. In fact, the heterocyclic moiety was necessary for a high-yielding asymmetric induction (Equation 67) <20050L1577, 2006OBC2685>. 

Asymmetric hydroxylation of chiral imides The (Z)-spdium enolates of the chiral imides 2 and 3 undergo asymmetric hydroxylation on reaction with 2-(phen-ylsulfonyl)-3-phenyloxaziridine (1). The products [(R)-4 and (S)-6] are solvo-lyzed to (R)- and (S)-a-hydroxy esters. This hydroxylation can also be effected with MoOPh, which is much less reactive than 1 but slightly more stereoselective. In general 1 is preferred to MoOPh because of the higher yields. 

These results were disputed, however, when Dehmlow questioned the reproducibility obtained when using catalysts 1 [12] and 2 [13]. In fact, Dehmlow reported the use of quaternary ammonium salt 3 for the asymmetric hydroxylation reaction, with promising levels of enantioselectivity [8d]. 

Complex (2) is an effective catalyst for the asymmetric hydroxylation of aromatic hydrocarbons with 2,6-dichloropyridine IV-oxide as terminal oxidant. Up to 76% ee was achieved for the catalytic hydroxylation of 4-ethyltoluene, 1,1-diethylindane, and benzylcyclopropane. Both electron-donating and -withdrawing substituents were found to accelerate the catalytic oxidation reaction. A large primary kinetic isotope effect (kH/kD = 11 at 298 K) was observed for the catalytic ethylbenzene-dio oxidation. A... 

The antibiotic ( + )-kjellmanianone (2) has been prepared by asymmetric hydroxylation of the sodium enolate of the P-keto ester 1 with several (camphoryl)oxaziri-dines. The highest enantioselectivity (68.5% ee) was obtained by use of the p-(trifluoromethyl)benzyl derivative 3.3... 

Electrophilic amination with oxaziridines 91S327. A-Sulfonyloxaziridines as reagents in asymmetric hydroxylation of eno-lates 92CRV919. 

The enantioselective synthesis of phthalide 227 (the (3 )-isomer), and other substituted phthalides, and the determination of their absolute configuration has been reported <2005CH218>. In a different approach to the same compounds, 2-alkylbenzoic acids were fed to microorganisms known to affect asymmetric hydroxylation. Lactonization of the resulting alcohols yielded the phthalides, used as scents in cosmetics and soaps <1997JPP10243794>. There is sufficient interest in these optically pure compounds for a chiral gas chromatography (GC) stationary phase to have been developed to quantify stereoisomeric mixtures. A silylated /3-CD was employed... 

N-Sulfonyloxaziridines are an important class of selective, neutral, and aprotic oxidizing reagents.11 Enantiopure N-sulfonyloxaziridines have been used in the asymmetric hydroxylation of enolates to enantiomerically enriched a-hydroxy carbonyl compounds,9 11-13 the asymmetric oxidation of sulfides to sulfoxides,14 1S selenides to selenoxides,16 sulfenimines to sulfinimines,17 and the epoxidation of alkenes.18... 

ASYMMETRIC HYDROXYLATION OF TETRALONE AND PROPIOPHENONE ENOLATES USING (CAMPHORYLSULFONYL)OXAZIRIDINES 1 AND 2... 

Extension of this procedure to provide a means of asymmetric hydroxylation has been the subject of more recent attention. Initially oxaziridines bearing a camphor-derived residue at nitrogen, for example... 

The success of Ae catalytic procedure bodes well for future application and furthennore bears some possibilities for asymmetric hydroxylation. ... 

L. Dorow, J. Am. Chem. Soc., 1985, 107, 4346, for oxaziridine-mediated asymmetric hydroxylation of chiral ester enolates. 

Terminal epoxides of high enantiopurity are among the most important chiral building blocks in enantioselective synthesis, because they are easily opened through nucleophilic substitution reactions. Furthermore, this procedure can be scaled to industrial levels with low catalyst loading. Chiral metal salen complexes have also been successfully applied to the asymmetric hydroxylation of C H bonds, asymmetric oxidation of sulfides, asymmetric aziridination of alkenes, and the asymmetric alkylation of keto esters to name a few. 

Extension of this procedure to provide a means of asymmetric hydroxylation has been the subject of more recent attention. Initially oxaziridines bearing a camphor-derived residue at nitrogen, for example (45), were considered. Relatively low levels of chiral induction were achieved and a more rigid compressed system was sought. Camphorsulfonyloxaziridines (46a and b) were subsequently shown to... 

Osmium tetroxide-mediated cis hydroxylation of a silyl enol ether has been demonstrated to produce the corresponding a-hydroxy ketone in moderate yield after exposure to an acidic work-up, e.g. (64) to (65). The success of the catalytic procedure bodes well for future application and furthermore bears some possibilities for asymmetric hydroxylation. ... 

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