Reduction diethylzinc

In addition to serving as a key stereochemical controlling element for synthesis of indinavir, the title compound has proven to be a remarkably versatile chiral ligand and auxiliary for a range of asymmetric transformations including Diels-Alder reactions, carbonyl reductions, diethylzinc additions to aldehydes, and enolate... 

Although the previous protocol suggests it is not necessary to deprotonate the sulfonamide prior to exposure to the zinc carbenoid, a experimentally simpler procedure can be envisioned wherein the alcohol and promoter are deprotonated in a single flask (Fig. 3.15). In protocol IV, the alcohol and promoter are combined in flask A and are treated with diethylzinc, thus forming the zinc alkoxide and zinc sulfonamide. In sub-protocol IVa, this solution is transferred to flask C which contains the zinc carbenoid. Sub-protocol IVb represents the reversed addition order. Sub-protocol IVa is not only found to be the superior protocol in this sub-set, it is found to out-perform all of the previous protocols Despite the persistence of the induction period, a large rate enhancement over the uncatalyzed process is observed. This considerable rate enhancement also translates to a reduction in the overall reaction time when compared to sub-protocols la and Ilia. Selectivity rises... 

In general, an ethyl(monoalkoxy)zinc is formed with amino alcohols6. Therefore, in the presence of an equimolar amount of chiral amino alcohol, a slow reduction of benzaldehyde to benzyl alcohol is observed rather than alkylation1. Alkylation only occurs with a ratio of diethylzinc to amino alcohol greater than equimolar. Consequently, a two-zinc species is postulated to be the actual catalyst1, n. 

Scheme 11 Reductive coupling of enynes using 59 and diethylzinc...

Ni(COD)2 alone catalyzes intramolecular alkylative cyclization of an alkynal with diethylzinc, while Ni(COD)2/PBu3 catalyzes reductive cyclization with the same zinc reagent (Scheme 87). 

In the conjugate addition of diethylzinc to enones catalyzed by copper reagent CuOTf or Cu(OTf)2 in the presence of 90, an ee of over 60% has been obtained. Study also shows that the actual catalyst in the reaction may be a Cu(I) species formed via in situ reduction of Cu(II) complexes. 

N-Methylation of 3 and reduction of the crystalline oxazolidinone 4 with lithium aluminum hydride was found to give a superior yield of DAIB (5) and a more easily purified product than exhaustive methylation of 2 with methyl iodide and reduction of the quaternary methiodide with Super-Hydride. Recently, a modified version of DAIB, 3-exo-morpholinoisoborneol MIB), was prepared by Nugent that is crystalline and that is reported to give alcohols in high enantiomeric excess from the reaction of diethylzinc with aldehydes. ... 

They have also developed a catalytic version of the reaction in which the chiral ligand DIPT was used in 20 mol% (379-381). In spite of the reduction of the amount of the chiral ligand, enantioselectivities of up to 93% ee were obtained in this work. The addition of a small amount of 1,4-dioxane proved to be crucial for the enantioselectivity of the reaction. A proposal for the reaction mechanism is outlined in Scheme 12.88. Allyl alcohol, hydroximoyl chloride 274 and diethylzinc react to form 276, which is mixed with the ligand and an additional amount of... 

On use as homogeneous catalysts in the asymmetric reductive alkylation of benzaldehyde with diethylzinc to form secondary alcohols, the corresponding dendritic titanium-TADDOL complexes having either chiral or achiral dendrons gave enantiomeric excesses (ee) of up to 98.5 1.5 at a conversion of 98.7% (for the catalyst with GO dendrons). With larger dendrons the reduction of the ee to 94.5 5.5 (G4) remained within reasonable limits, while the drop in conversion to 46.8% (G4) proved to be drastic. In comparison, the unsubstituted Ti-TAD-DOL complex gave an ee of 99 1 with complete conversion. This negative den-... 

Whereas iV-tosylimines do not coordinate diethylzinc well in polar solvents (and thus tend to give ethylated product), solvents such as toluene favour coordination, leading to reduction of the imine to secondary amines under mild conditions, via a /3-hydrogen transfer mechanism 48... 

See also reduction of imines with diethylzinc under Addition of Organometallics above, and ionic hydrogenation of Iminium Species below. 

Cyanopyridines undergo titanium-mediated reductive cyclopropanation to give pyridylcyclopropylamines in good yield <20030L753>. Both 2- and 3-cyanopyridine react with the titanium species 81 formed from diethylzinc and methyltriisopropyloxytitanium in the presence of lithium isopropoxide to give the cyclopropylamine product in 80% and 82% yield, respectively (Equation 55). 

According to Jenkins diethylzinc has no effect on molar mass [157]. In contrast to the negative result published by Jenkins there are reports from two other sources on the successful use of diethyl zinc [180-182,466,467]. These differences are either due to different catalyst systems or are due to differences in the addition order of catalyst components. Strong evidence in favor of molar mass control by diethyl zinc was provided by Lynch who used NdV/MgR2-based catalyst systems [466,467]. In combination with NdV/DIBAH/EASC the use of ZnEt2 also resulted in a reduction of molar mass [ 180-182]. A careful study revealed that the formal number of polymer chains (pexp) formed per Nd atom increases with increasing nznEt2/ Ndv-ratios (Table 24). 

The course of the reactions was rationalized by initial reduction of the Pd(II) precatalyst to a Pd(0) species 190A by diethylzinc. This electron-rich complex reduces the alkyl iodide 187 to a radical 187 A, which undergoes cyclization to the alkene unit. The diastereoselectivity of the cyclizations can be explained by a Beckwith-Houk... 

D. The use of chiral oxazaborolidines as enantioselective catalysts for the reduction of prochiral ketones, imines, and oximes, the reduction of 2-pyranones to afford chiral biaryls, the addition of diethylzinc to aldehydes, the asymmetric hydroboration, the Diels-Alder reaction, and the aldol reaction has recently been reviewed.15b d The yield and enantioselectivity of reductions using stoichiometric or catalytic amounts of the oxazaborolidine-borane complex are equal to or greater than those obtained using the free oxazaborolidine.13 The above procedure demonstrates the catalytic use of the oxazaborolidine-borane complex for the enantioselective reduction of 1-indanone. The enantiomeric purity of the crude product is 97.8%. A... 

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