Dihydroquinine acetate

Solubility p-C C6ii4C(0)- sol CH2CI2, Et20, EtOH, EtOAc. 

Form Supplied in the -chlorobenzoate is available as a white foam. 

Preparative Methods the acetate is prepared from dihydroquinine and the p-chlorobenzoate is commercially available. The phthalazine-derived bis(dihydroquinine) ligand is commercially available. A formulation of the standard reactants for the asymmetric dihydroxylation (AD-mix-a) on the small scale has been developed and is commercially available. AD-mix-a (1 kg) consists of potassium osmate (0.52 g), the phthalazine-derived ligand (5.52 g), K3pe(CN)6 (700 g), and powdered K2CO3 (294 g). 

Purification dihydroquinine / -chlorobenzoate is recovered after a dihydroxylation reaction using the same method as that described for Dihydroquinidine Acetate. 

Handling, Storage, and Precautions toxic use in a fume hood. 

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In 1980, Hengtges and Sharpless published a seminal report that dihydroxylation occurred in a good enantioselective manner when the reaction was carried out in the presence of a chiral amine, dihydroqunidine acetate (DHQD-Ac) or dihydroquinine acetate (DHQ-Ac). DHQD and DHQ are diastereomers to each other, but they behaved like enantiomers in this reaction (Scheme 42).167... 

In Figure 14.14 we have depicted the most striking result from the 1980 paper involving /rara-stilbenc as the substrate and dihydroquinine acetate. After addition the osmate ester was decomposed by reduction with UAIH4, a common procedure in the early days, to give the threo-dio. A diastereomer of the ligand, dihydroquinidine acetate, gave similar e.e. but the opposite enantiomer. The enantioselectivity was 83%. 

ASYMMETRIC DIHYDROX YLATION Osmium tetroxide-Dihydroquinine acetate. 

DIHYDROXYLATION Osmium tetroxide-Dihydroquinine acetate. Osmium tetrox-ide-Diphenyl selenoxide. Osmium tetroxide-Trimethylamine N-oxide-Pyiidine. Thallium(l) acetate-iodine. Triphenylmethylphosphonium permanganate. 

In the second approach, a chiral nitrogen-containing compound has most often been used as the ligand to achieve enantioselectivity. Thus, oxidation of ( )-stilbene (22 equation 9) with a stoichiometric quantity of osmium tetroxide in toluene at room temperature, in the presence of dihydroquinine acetate (23), yielded r/ireo-hydrobenzoins (24) after reductive hydrolysis, with an enantiomeric excess of 83.2% in favor of the (15,25)-(-)-isomer performing the reaction at -78 C increased the eiuuitiomeric excess to 89.7%. 

Protected a,p-dihydroxy aldehydes have been prepared by oxidation of acetals of a,p-unsaturated aldehydes with osmium tetroxide in the presence of (23), and a remarkable level of enantioselection (ee 90%) thereby achieved. Oxidation of chiral acetals of a, -unsaturated aldehydes in which chirality resides in the noncarbonyl moiety with osmium tetroxide-dihydroquinine acetate (or dihydroquinidine acetate) may be regarded as a process in which double stereoselection is at work and a high dia-stereoisomeric ratio of products may be obtained. 

Related Reagents. (/ )- ,l -Bi-2,2 -naphthotitanium Dichloride (/ )- ,T-Bi-2,2 -naphthotitanium Diisopropoxide Dihydroquinine Acetate (15,9.S)-l,9-Bis [(r-butyl)dimethylsilyloxy]-methyl -5-cyanosemicorr in 2,2-Dimethyl-a,a,a, a -tetraphenyl-1,3-dioxolane-4,5-dimethanolatotitanium Diiso-... 

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