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And diethylzinc

The cyclopropanation of 1-trimethylsilyloxycyclohexene in the present procedure is accomplished by reaction with diiodomethane and diethylzinc in ethyl ether." This modification of the usual Simmons-Smith reaction in which diiodomethane and activated zinc are used has the advantage of being homogeneous and is often more effective for the cyclopropanation of olefins such as enol ethers which polymerize readily. However, in the case of trimethylsilyl enol ethers, the heterogeneous procedures with either zinc-copper couple or zinc-silver couple are also successful. Attempts by the checkers to carry out Part B in benzene or toluene at reflux instead of ethyl ether afforded the trimethylsilyl ether of 2-methylenecyclohexanol, evidently owing to zinc iodide-catalyzed isomerization of the initially formed cyclopropyl ether. The preparation of l-trimethylsilyloxybicyclo[4.1.0]heptane by cyclopropanation with diethylzinc and chloroiodomethane in the presence of oxygen has been reported. "... [Pg.60]

The use of cyclic a,p-unsaturated ketones as starting materials in the enantioselective addition of dimethyl- and diethylzinc reagents catalysed by the HOCSAC ligand was introduced by Walsh and Jeon, in 2003. As shown in Scheme 4.16, the corresponding cyclic tertiary alcohols were formed in high enantioselectivities of up to 99% ee. [Pg.169]

Further optimization of this reaction was carried out with TFE as an achiral adduct, since reaction with TFE is much faster than that with neopentyl alcohol. We found that dimethyl- and diethylzinc were equally effective, and the chiral zinc reagent could be prepared by mixing the chiral modifier, the achiral alcohol and dialkylzinc reagent in any order without affecting the conversion and selectivity of the reaction. However, the ratio of chiral to achiral modifier does affect the efficiency of the reaction. Less than 1 equiv of the chiral modifier lowered the ee %. For example with 0.8 equiv of 46 the enantiomeric excess of 53 was only 58.8% but with 1 equiv of 46 it was increased to 95.6%. Reaction temperature has a little effect on the enantiomeric excess. Reactions with zinc alkoxide derived for 46 and TFE gave 53 with 99.2% ee at 0°C and 94.0% ee at 40°C. [Pg.33]

Scheme 11 Reductive coupling of enynes using 59 and diethylzinc... Scheme 11 Reductive coupling of enynes using 59 and diethylzinc...
The spectra of flames from spontaneous interaction of ozone with dimethylzinc and diethylzinc in a flow system have been studied. [Pg.1867]

Dimethyl- and diethylzinc reacted with dimethylpyrrole- and mesityl-substituted cyclopentadiene ligands to give monocyclopentadienyl(methyl)zinc and -ethyl(zinc) compounds. These products then formed, Scheme 20, crystalline adducts with tetramethylethylenediamine (TMEDA) such as 24, whose solid-state structure is shown in Figure 11. [Pg.325]

Organophosphonates are isoelectronic with organotrisiloxides. Like zinc siloxides and zinc siloxanes, zinc phosphonates are actively investigated as porous materials, for applications in catalysis, as molecular sieves, and for electronic devices. Dimethyl- and diethylzinc reacted with / //-butylphosphonic acid in THF solution to furnish,... [Pg.368]

The interactions of dimethyl- and diethylzinc with bulky tris(hydroxyphenyl)methanes, Scheme 86, yielded, depending on the reaction conditions, a variety of alkylzinc alkoxides, featuring two-, three-, and four-coordinate zinc centers. These polynuclear compounds (Figure 63 shows the trinuclear ethylzinc derivative 136) are relatively poor catalysts for the co-polymerization of cyclohexene oxide and carbon dioxide.197... [Pg.369]

We have already mentioned that the mixed alkyl halide compounds of aluminum dimerize, and the solubility parameters shown in Table 12.1 for these compounds are consistent with that assessment. The solubility parameters for triethylboron and diethylzinc are 15.4 and 18.2 in J cm 3/2, respectively. These values are indicative of liquids that are not strongly associated, which is known to be the case. [Pg.407]

Both the aldehyde and diethylzinc are activated by the zinc amide, and the ethyl group transformation from diethylzinc to aldehyde furnishes the highly enantioselective alkylation of aromatic aldehydes. [Pg.115]

Stannyl radicals are usually generated by homolytic substitution at hydrogen in a tin hydride, or at tin in a distannane, or, conjugatively, at the y-carbon atom in an allylstannane.453 The initiator is commonly AIBN at ca. 80 °C. In the presence of a trace of air, organoboranes are oxidized by a radical chain mechanism, and triethylborane is now commonly used as an initiator at temperatures down to —78°C,519 and it can be used in aqueous solution.520 9-Borabicyclo[3.3.1]nonane (9-BBN) has similarly been used to initiate the reaction of tin hydrides at 0 and —78°C,521 and diethylzinc works in the same way.522... [Pg.864]

Figure 3.1. Chiral ligands that exhibit >95% ee in the reaction between 2-cyclohexen-l-one and diethylzinc under copper catalysis. Figure 3.1. Chiral ligands that exhibit >95% ee in the reaction between 2-cyclohexen-l-one and diethylzinc under copper catalysis.
The same dendritic ligands were used for the addition of disopropylzinc and diethylzinc to aldehydes (phenyl, 2-naphthyl, / -tolyl) 46). The two ligands were equally selective for the (J )-alcohol product (77% < ee 86%, depending on the substrate). Dendrimer 53 was recovered after the reaction between diethylzinc and benzaldehyde and was reused in a consecutive run, giving the same enantioselec-tivity. [Pg.115]

Dramatic chiral amplification is observed in alkylations catalyzed by partially resolved DAIB7 Reaction of benzaldehyde and diethylzinc in toluene containing 8 mol % of (2S)-DAIB of 15% ee leads to (S)-1-phenyl-1-propanol in 95% ee, a value close to the 98% ee obtained with enantiomerically pure (2S)-DAIB. [Pg.73]

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... [Pg.883]

Representative results are shown in Fig. 2.1.2.1. Both reactions with mixtures of diphenylzinc and diethylzinc and those with pure diphenylzinc are catalyzed by ferrocene 9 as indicated by the comparisons between curves A and C as well as B and D, respectively. Apparently the reaction becomes slower when the mixture of the zinc reagents is applied (curve A versus curve B). We presume that this effect is - as hoped - due to a less pronounced background reaction as well as to a modification of the aryl source (potentially PhZnEt or complexes thereof). Consequently, a better control of the enantioselectivity at the expense of the reaction rate is observed. [Pg.183]

So far, attempts to expand the substrate scope further by modifying the aryl transfer agent have remained unsuccessful. Thus, imine addition reactions with arylzinc species other than the one prepared in situ by mixing diphenylzinc and diethylzinc still deserve attention, and will be developed in the near future. [Pg.191]

At low temperatures in inert solvents (such as methylene dichloride) a controlled polymerization can be effected using various acids and alkylating agents. These initiators include boron trifluoride etherate, triethylaluminum, trityl hexachloroantimonate, triethylam-monium hexachloroantimonate, diethyloxonium hexafluoroantimonate, p-toluenesulfonic acid and diethylzinc or cadmium-1,2-dioI complexes. Crystalline, high molecular weight... [Pg.382]

Asymmetric epoxidation of a,jS-unsaturated ketones represents an efficient method for the preparation of optically active a,jS-epoxy ketonesJ Recently, a new and very efficient catalytic system for enantioselective epoxidation of ( )-a,jS-enones to the corresponding trans-epoxy ketones has been developed based on a BlNOL-zinc complexJ Very high yields and excellent diastereo- and enantioselectivities are achieved at room temperature using cumene hydroperoxide (CMHP) as the terminal oxidant and performing the reaction in diethyl ether. A combination of enantio-merically pure BINOL and diethylzinc readily affords the active catalyst in situ (Figure 6.13). ... [Pg.249]

In a recent synthesis of a mixed zinc/cadmium telluride alloy, a mixture of dimethyl-cadmium and diethylzinc was employed. The original authors interpreted the results by assuming that the redistribution reaction 3 is essentially thermoneutral since the difference between the enthalpies of formation for the symmetrical dialkylzincs is small. [Pg.143]

Functionalized zinc carbenoids have been prepared from diiodoalkanes and diethylzinc and used in stereoselective transformations, but their use is limited by the availability of the diiodoalkane" ° and the stability of the resulting zinc carbenoid. Alternatively, the reaction of a diazoalkane with Znl2 can be used to access complex zinc carbenoids, but with modest efficiency (equation 9) . ... [Pg.241]

Diethylzinc, one of the first organometallic compounds to be isolated (Fran-kland, 1849), epitomizes these characteristics. The compound is easily prepared by heating powdered zinc or zinc-copper alloy with ethyl iodide under an atmosphere of dry nitrogen or CO2 (the initial product is actually C2H5ZnI, which disproportionates on distillation to zinc iodide and diethylzinc) ... [Pg.392]

Amino Alcohol Catalyzed Alkylation. (—)-3-exo-(Dimethylamino)-isobomeol [( —)-DAIB] is a sterically restrained jS-dialkylamino alcohol that has proven to be an extremely efficient catalyst 13). For instance, in the presence of 2 mol % of (—)-DAIB, the reaction of benzaldehyde and diethylzinc proceeds smoothly to give, after aqueous workup, (5)-1 -phenyl-1 -propanol in 98% ee and in 97% yield along with a small amount of benzyl alcohol (Scheme 9). Nonpolar solvents such as toluene, hexane, ether, or their mixtures produce satisfactory results. The optical yield in toluene is affected by temperature and decreases from 98% at —20°C to less than 95% at 50°C. The catalytic enantioselective reaction has been extended to a range of alkylating agents and aldehyde substrates, which are summarized in Scheme 10 (75). p-Substituted ben-... [Pg.334]

Amplification of Chirality. Perhaps the most striking of the nonclas-sical aspects that emerge from the enantioselective alkylation is the phenomenon illustrated in Scheme 22 (3, 14, 16, 20k, 40). A prominent nonlinear relation that allows for catalytic chiral amplification exists between the enantiomeric purity of the chiral auxiliary and the enantiomeric purity of the methylation or ethylation product (Scheme 23). Typically, when benzaldehyde and diethylzinc react in the presence of 8 mol % of (-)-DAIB of only 15% ee [(-) (+) = 57.5 42.5], the S ethylation product is obtained in 95% ee. This enantiomeric excess is close to that obtained with enantiomerically pure (—)-DAIB (98%). Evidently, chiral and achiral catalyst systems compete in the same reaction. The extent of the chiral amplification is influenced by many factors including the concentration of dialkylzincs, benzaldehyde, and chiral... [Pg.340]


See other pages where And diethylzinc is mentioned: [Pg.116]    [Pg.116]    [Pg.236]    [Pg.175]    [Pg.213]    [Pg.315]    [Pg.326]    [Pg.356]    [Pg.37]    [Pg.16]    [Pg.439]    [Pg.641]    [Pg.212]    [Pg.211]    [Pg.138]    [Pg.139]    [Pg.246]    [Pg.569]    [Pg.139]    [Pg.140]    [Pg.337]    [Pg.119]   
See also in sourсe #XX -- [ Pg.1089 ]




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Diethylzinc

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