Preparation with zinc/copper couple

Monofluoroalkenes have been prepared by the addition of fluoromethylene-triphenylphosphorane generated m situ by treatment of fluoroiodomethyltri-phenylphosphomum iodide with zinc-copper couple in dimethylformamtde [49] (equation 47) (Table 181. 

The importance of solvent effects in the preparation of perfluoroalkyzinc reagents is further illustrated in the reaction of perfluoroalkyl iodides with zinc-copper couple. In DMSO, DMF, and HMPA, the main products are the fluo-roolefins The formation of the fluoroolefin is facilitated when the reaction is carried out in the presence of potassium thiocyanate [30] (equation 21)... 

We have found that the method used to prepare the zinc-copper couple is an important variable in determining the efficiency and rate of these reactions. Optimal results are achieved using a couple prepared by brief 2 min) exposure of commercial zinc dust to twice the amount (0.06 equiv) of copper sulfate employed in the previous studies.We have also found that the cycloadditions proceed with equal efficiency and more conveniently by... 

DeCamp et al.t19l synthesized the lactone intermediate of the 1-hydroxyethylene isostere with high yields and stereoselectivity. As summarized in Scheme 10 (Section 10.6.2), the titanium homoenolate is prepared from ethyl 3-iodopropionate. The iodide is metalated with zinc/copper couple to give the iodozinc homoenolate species. The alkyltitanium homoenolate is then generated by transmetalation of the iodozinc precursor with one of the several chlorotitanium isopropoxide species. The resulting titanium homoenolate reacts with a N-protected a-amino aldehyde, leading to a mixture of 45-diastereomers. In the last step, the product is lactonized. 

The chloro nitroso adducts of the ( -protected glycals were converted, via the intermediate oximes, to 2-amino-2-deoxy sugars48,50,53,59 the overall oxyamination of glycals is hence accomplished. Amines of the opposite configuration are prepared depending on the method of reduction. The chloro nitroso adducts can be directly treated with zinc-copper couple in acetic acid, or can be first converted to fully acetylated oximes which are then catalytically hydrogenated. 

Cyclopropanation with zinc-copper couple and diiodomethane is still the method of choice for preparing precursor cyclopropyl compounds for further studies, as in the case of mercury(II)-mediated cyclization of (hydroperoxyalkyl)cyclopropanes." ... 

Related reagent, ethyUodomethyliinc, QHjZnCHsl.12 Mol. wt. 235.38. The leagcnt is prepared by the reaction of ethyl iodide with zinc-copper couple in ihxoliite ether to give ethylzinc iodide (I). probably in equilibrium with diethyl-llttc and zinc iodide. This stock solution can be stored at room temperature for a... 

Preparative Methods several methods for the preparation of bis[(trimethylsilyl)methyl]zinc have been reported. Addition of powdered anhydrous zinc(II) chloride to a solution of [(trimethylsilyl)methyl]magnesium chloride in diethyl ether at 0 °C and subsequent stirring for 4 days at room temperature affords the title compound in 90% yield after fractional distillation. A second route consists of the reaction of (iodomethyl)tri-methylsilane with zinc/copper couple (prepared by reduction of CuO with dihydrogen in the presence of zinc dust) at reflux for 3 h and affords the title compound in 56% yield. Bis[(trimethylsilyl)methyl]zinc can also be prepared quantitatively by reacting bis[(trimethylsilyl)methyl]mercury with an excess of zinc at ambient conditions. ... 

Organozinc compounds in which the ester group is farther removed from the carbanion center can also be prepared. This would not be possible for the more reactive lithium or magnesium reagents. The y-, and 5-esters can be made by reaction of the corresponding iodo esters with zinc-copper couple ... 

The natural product (—)-hyoscyamine 12 was readily prepared in four simple steps from diastereoisomers 7 and 8 (Scheme 19.6). Treatment of 7 and 8 with zinc-copper couple followed by ketone reduction with excess DIBAL gave 6,7-dehydrotropine 11 stereoselectively in 92% yield for the two steps. The acylation of 11 with 0-acetyltropyl chloride and deprotection with hydrochloric acid gave 12 in 88% yield for the two steps. The intermediate 11 has proven to be a versatile intermediate, allowing access to a variety of important tropane alkaloids. 

An organozmc compound that occupies a special niche m organic synthesis is lodo methyhinc iodide (ICH2ZnI) It is prepared by the reaction of zinc-copper couple [Zn(Cu) zinc that has had its surface activated with a little copper] with diiodomethane m diethyl ether... 

In 1958 Simmons and Smith described a new and general synthesis of cyclopropanes by treatment of olefins with a reagent prepared from methylene iodide and a zinc-copper couple in ether solution. 

With special techniques for the activation of the metal—e.g. for removal of the oxide layer, and the preparation of finely dispersed metal—the scope of the Refor-matsky reaction has been broadened, and yields have been markedly improved." The attempted activation of zinc by treatment with iodine or dibromomethane, or washing with dilute hydrochloric acid prior to use, often is only moderately successful. Much more effective is the use of special alloys—e.g. zinc-copper couple, or the reduction of zinc halides using potassium (the so-called Rieke procedure ) or potassium graphite. The application of ultrasound has also been reported. ... 

B) The preparation of (cis-1,2-epoxypropyi)phosphonic acid [ (1 -chloroethoxy )chloro-methyl] phosphonic acid (1.0 g) is added with stirring to tetrahydrofuran (50 ml) to which has been added a crystal of iodine and a zinc-copper couple (15.0 g). The mixture is then heated under reflux for 24 hr and the resulting solution filtered to yield (cis-1,2-epoxy propyl )-phosphonic acid. 

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. "... 

B. Cydopropylbenzene. In a 1-1. three-necked flask equipped, with a stirrer and a thermometer extending into the flask but free from the stirrer are placed 500 ml. of redistilled dimethyl-formamide and zinc-copper couple prepared from 131 g. (2 g. atoms) of zinc (Note 8). The mixture is cooled to 7° in an ice bath, and 1,3-dibromo-l-phenylpropane is added to the stirred mixture at a rate sufficient to maintain the reaction temperature at 7-9° (Note 9). The mixture is stirred for 30 minutes after the addition is completed, poured into 1 1. of water, and then steam-distilled until the condensate is homogeneous or 11. of water has been collected. The organic layer is separated from the distillate, and the aqueous layer is extracted with three 100-ml. portions of ether. The combined organic portions are washed with four 50-ml. portions of water and dried over anhydrous potassium carbonate. The ether is removed by distillation at atmospheric pressure at water bath temperature. The residue is distilled to give 88-100 g. (75-85%) of cydopropylbenzene, b.p. 170-175° (Note 10), 26d 1.5306-1.5318. 

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