Zinc iodide preparation

Recently, the required heteroaromatic organozinc halides for the Negishi reaction have also been prepared using microwave irradiation [23]. Suna reported that a Zn - Cu couple (activated Zn), prepared using a slightly modified LeGoff procedure from Zn dust and cupric acetate monohydrate, allowed the smooth preparation of (3-pyridinyl)zinc iodide and (2-thienyl)zinc iodide... 

A completely different way of preparing isocyanides involves the reaction of epoxides or oxetanes with trimethylsilyl cyanide and zinc iodide, for example, ... 

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. "... 

Aziridines have been synthesized, albeit in low yield, by copper-catalyzed decomposition of ethyl diazoacetate in the presence of an inline 260). It seems that such a carbenoid cyclopropanation reaction has not been realized with other diazo compounds. The recently described preparation of 1,2,3-trisubstituted aziridines by reaction of phenyldiazomethane with N-alkyl aldimines or ketimines in the presence of zinc iodide 261 > most certainly does not proceed through carbenoid intermediates rather, the metal salt serves to activate the imine to nucleophilic attack from the diazo carbon. Replacement of Znl2 by one of the traditional copper catalysts resulted in formation of imidazoline derivatives via an intermediate azomethine ylide261). 

The general utility of the oxidative addition of functionalized organic halides to zinc was demonstrated by the formation of organozinc iodides 28 from protected (3- and 7-amino acids (Scheme 26).73 The organozinc iodides prepared in this manner were neither sufficiently stable nor sufficiently reactive in THF, but excellent yields were obtained in more polar aprotic solvents, such as DMF and DMSO. 

In the preparation of iodides, but not bromides, PMHS may be substituted for the TMDO. Chlorides can be obtained if thionyl chloride and zinc iodide are added to suppress the formation of symmetrical ethers.314 An example of this type of reductive chlorination is shown by the TMDO-mediated conversion of p-tolualdehyde into p-methylbenzyl chloride (Eq. 201).313 To obtain chlorides from aldehydes having electron-withdrawing groups such as nitro or carbomethoxy, the initial reaction is first carried out at —70° and the mixture is then heated to reflux in order to reduce the formation of symmetrical ether by-products. Zinc chloride is substituted for zinc iodide for the synthesis of chlorides of substrates with electron-donating groups such as methoxy and hydroxy.314... 

Ammino-zinc Iodides.—These are prepared in the same way as those of zinc chloride. Pentammino-zinc iodide, [Zn(NH3)5]X2, and hc.mmmino-zinc iodide, [Zn(NH3)G I2, are easily obtained. 

Tetrammino-zinc Iodide, [Zn(NH3)4]I2, is prepared by dissolving zinc iodide in aqueous ammonia and evaporating the solution, when white glistening leaflets containing no water separate. The crystals are stable in air but decompose on heating. They dissolve easily in acids and are decomposed by cold water. 

By use of aliphatic zinc iodides, in toluene solution, mixed aromatic-aliphatic azo compounds have also been prepared [45b]. Reported properties are... 

Shortly after Simmons and Smith s seminal publication, "Wittig and coworkers reported that the treatment of zinc iodide with either 1 or 2 equiv of diazomethane also produces IZnCH2l or the analogous bis(iodomethyl)zinc reagent [Zn(CH2l)2]- However, this method for the preparation of the reagent has been far eclipsed by the others. 

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) ... 

Preparation of Zinc Iodide in Absolute Ether. Assemble an apparatus (see Fig. 119a), replacing dropping funnel 4 with a glass stopper provided with a ground-glass joint. Put 3 g of powdered zinc,... 

The method has been applied by the submitters2 to the preparation of cyclohexylmethylpropiolaldehyde diethyl acetal (54% yield) from cyclohexylmethylacetylene and triethyl orthoformate of phenylethynyl n-butyl dimethyl ketal (40% yield) from phenylacetylene and trimethyl -orthovalerate and of phenylethynyl methyl diethyl ketal (34% yield) from phenylacetylene and triethyl orthoacetate. w-B utylpropiolaldehyde diethyl acetal was isolated in 32% yield by heating an equimolar mixture of 1-hexyne and triethyl orthoformate containing catalytic amounts of a zinc chloride-zinc iodide catalyst under autogenous pressure at 190° for 3 hours. 

I S-Cycloalkanediones.1 In the presence of a zinc reagent prepared from Zn-Cu and this alkyl iodide, chloromethyl methyl ether reacts with 1,2-bis(trimethyl-silyloxy)cycloalkenes (I) to form 2-hydroxy-2-methoxymcthylcycloalkanones (2) (cf 8, 415). Ring-enlarged 1,3-cycloalkanediones (3) are formed from (2) by treatment with acid. 

With the development of the cross coupling methodology, many 6-C-substituted purines have been prepared in the past decade. Thus, 6 halopurine derivatives react with arylmagnesium halides,25 alkyl(aryl)zinc or tin reagents,26 trialkylaluminum,27 or alkylcuprates28 to give the 6-alkylpurine derivatives. Also a reverse approach based on the reaction of purine-6-zinc iodide with aryl or vinyl halides has recently been described.29 For the synthesis of 6-arylpurines, an alternative approach makes use of radical photochemical reactions of adenine derivatives with aromatic compounds,30 but this method is very unselective and for substituted benzenes, mixtures of ortho-, meta-, and para substituted derivatives were obtained. 

Allylcopper/zinc reagents can be prepared directly by reaction of vinyl copper reagents with (iodomethyl)zinc iodide, the Simmons-Smith reagent. These allylcopper/zinc reagents do not couple with an alkyl iodide or benzyl bromide, but react readily with electrophiles such as aldehydes, ketones, or imines.3 This approach to organodimetallic reagents is apparently limited (see Iodomethylzinc iodide, this volume). 

Different pyridinyl pyrimidines were prepared with Negishi couplings (Scheme 72). The reported procedure took advantage of the lower hygroscop-icity and higher solubility of zinc iodide in ethereal solvents, as compared... 

The application of organozinc iodides prepared in THF is illustrated in Protocols 4 and 5, which describe the palladium catalysed cross-coupling of a serine-derived organozinc iodide with a vinyl iodide, and the palladium catalysed carbonylative cross-coupling of another serine-derived organozinc iodide with a functionalized aromatic iodide. In the reaction with the vinyl iodide, it is important to transfer the solution of the organozinc iodide from the residual zinc, since this can react unproductively with the electrophile. In the case of the carbonylative coupling with the functionalized aromatic iodide, such a transfer is unnecessary, since the zinc does not react with the electrophile under the reaction conditions. These two protocols also illustrate how to conduct such reactions on different scales. 

Palladium catalysed coupling reaction of a heteroaromatic zinc compound with a functionalized aryl iodide preparation of N-benzyl-6-(4-ethylcarboxyphenyi)-purine33... 

Finally, Wittig20 reported that treatment of zinc iodide with either one or two equivalents of diazomethane was an alternative method to prepare IZnCH2I (Table 13.1, entry 3a) or the analogous his(iodomethyl)zinc reagent [(Zn(CH2I)2] (Table 13.1, entry 3b). This method, however, has not attracted much attention from synthetic organic chemists due to the hazards involved when diazomethane is used on multigram scale.21... 

Fig (16) The enone (131), prepared from (130) is alkylated with iodide (133) to obtain the product (134). It reacts with trimethylsilyl cyanide and zinc iodide. The resulting product (135) is converted to tricyclic compound (136) by heating with hydrochloric acid and ethanol. 

The remaining unreacted (RJ-20 can be trapped with an aldehyde such as pivalaldehyde giving the chiral homopro-pargylic alcohol in 87.5% ee.74 This kinetic resolution has been used to prepare anti/inti-vicinal amino diols in > 95% ee and dr > 40 l.75 In general, diorganozincs are more easily prepared in optically pure form. On another hand, secondary zinc reagents prepared by the direct zinc insertion to secondary alkyl iodides are obtained without stereoselectivity (Scheme 4).76... 

Unsymmetrical alkyl phenyl tellurium derivatives were prepared in good yields from phenyl trimethylsilyl tellurium and epoxides, carboxylic acid esters, and linear or cyclic ethers under very mild conditions. In these reactions, which proceed in dichloromethane in the presence of a catalytic amount of zinc iodide, a carbon-oxygen single bond is cleaved. The highly nucleophilic benzenetellurolate binds to the carbon fragment, whereas the trimethylsilyl group becomes linked to the oxygen. 

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