Diethyl -tartarate

SHARPLESS Asymmetne Epoxidation EnanlioselectK/e epoxidation of altyl alcohois by means of Irtanlum a5(oxide, (+) or () diethyl tartarate (OET) and t butyl hydroperoxide (TBHP)... 

Cotton etal. [14] described an asymmetric synthesis of esomeprazole. Esomeprazole, the (S)-enantiomer of omeprazole, was synthesized via asymmetric oxidation of prochiral sulfide 5-methoxy-2-[[(4-methoxy-3,5-dimethyl pyridin-2-yl)methyl]thio]-lH-benzimidazole 1. The asymmetric oxidation was achieved by titanium-mediated oxidation with cumene hydroperoxide in the presence of (S,S)-diethyl tartarate (DET). The enan-tioselectivity was provided by preparing the titanium complex in the presence of sulfide 1 at an elevated temperature and/or during a prolonged preparation time and by performing the oxidation of sulfide 1 in the presence of amine. An enantioselectivity of 94% ee was obtained using this method. 

N-Acetyl-(R)-phenylalanine 2. The rhodium catalyst was obtained by adding (R,R)-DIOP (from diethyl tartarate) to a benzene solution of [RhCI (cyclooctene) under Ar and stirring for 15 min. A solution of the catalyst (1 mmol in EtOH PhH 4 1) was introduced under H2 to a solution of a-N-acetylamino- / -phenylacrylic acid 1 (molar ratio catalyst substrate 1 540). After hydrogenation at 1.1 bar, the solvent was evaporated, the residue was dissolved in 0.5N NaOH, the catalyst was filtered and the solution acidified and concentarted to dryness to afford 2 in 90% yield and 82% e,e. 

Synthesis from L-threitol The L-threitol derivative 24, obtained from D-(-)-diethyl tartarate in three steps and 90% overall yield, was used as a starting material for the synthesis of nectrisine (1) (Scheme 5). " Swern oxidation of 24 produced the L-threose derivative 25, which was transformed into the aminonitrile 26 in 96% overall yield from 24, as an inseparable diastereomeric mixture. Removal of the silyl protecting group from 26 followed by oxidation of the resulting primary hydroxyl group with TPAP afforded the lactam 27, which was treated with sodium methoxide to produce the methyl ester 28 in 62% yield from 26. Lithium borohydride reduction of 28 afforded a chromatographically separable mixture of the lactams 29 and 30 in a ratio of 56 44 and 87% total yield. Silylation... 

Oxidation of sulfides has been performed by TBHP in anhydrous conditions with an excess of diethyl tartarate (4 equivalents) [59]. Modena used 1,2-dichloroethane or toluene as solvent at -20°C. Some examples are listed in Table 1.3. As with the Kagan reagent, a high ee (88%) is obtained for the sulfoxidation of methyl p-tolyl sulfide in 1,2-dichloroethane, but the ee drops to 64% in toluene. 

Diethyl tartarate Pervatech silica Hollow fibers 85 Amberlyst 15 PER + ESU (parallel, series) and PER + ISU Nemec and Van Gemert (2005)... 

The in situ catalysts formed from diethyl tartarate (DET) and titanium(IV) isopropoxide catalyze the asymmetric epoxidation reactions (72). The seminal work of Sharpless has been applied for a great variety of synthetic reactions. (The replacement of titanium with zirconium, hafnium, or thallium does not improve the chiral efficiency)... 

The Sharpless epoxidation is another example of an enantioselective reaction achieved by using a chiral catalyst. In this reaction, a peroxide (tert-butylhydroperoxide) delivers its oxygen to only one side of the double bond of an allylic alcohol, in the presence of a metal catalyst (titanium(IV) isopropoxide) and a chiral organic molecule (diethyl tartarate DET). 

The structure of the epoxide depends on which isomer of diethyl tartarate is used. (See Table 4.2 on page 175.)... 

Sharpless asymmetric epoxidation (SAE) is the epoxidation of allylic alcohols into asymmetric epoxides in high chiral purity (high enantioselectiv-ity). Transition metal catalyst Ti(OPr ) with chiral additive, diethyl tartarate (DET), generates chiral catalyst (Scheme 9.40) which is responsible for the enantioselective outcome, while, tert-butyl hydroperoxide (TBHP) serves as an oxidant. Although, this eatalytic system holds disadvantage of low turnover number (TON) with potential safety coneems for using concentrated solutions of peroxides, the reaction has nevertheless been extensively used in pharmaceutical industry [76]. 

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