Zinc iodide catalyst

Zinc iodide catalysts are also known. Desulfonylative iodination of naphthalenesulfonyl chlorides has been carried out by treatment with zinc iodide in the presence of a palladium(II) catalyst.642... 

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. 

No catalyst employed zinc iodide catalyst used in all other cases. Yield determined by GLC analysis. 

Acetylene additions Aluminum chloride. Dimethylsilylazine. Simmons-Smith reagent Thiolacetic acid. Zinc iodide (catalyst). 

Technical grade zinc cyanide was used as supplied by Matheson, Coleman and Bell. Other Lewis acids, notably aluminum chloride, zinc bromide, and zinc iodide may be used as catalysts for the reaction. 

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). 

In a related three-component reaction procedure, aryl methyl ketones 724 have been combined with aryl aldehydes 725 and urea 726 at room temperature, using trimethylsilyl iodide as catalyst, to give 4,6-diaryl-3,4-dihydro-2(177)-pyrimidinones 727 <2005HCA2996>. A procedure using zinc iodide and microwave irradiation gave similar products <2007T1981>. 

The submitters report that zinc nitrate appears to be equivalent to zinc iodide as a catalyst and that zinc chloride (commercial anhydrous grade) is satisfactory but requires 2-3 hours of heating and gives 64-70% yield. 

Methanol can be converted to hydrocarbons over acidic catalysts. However, with the exception of some zeolites, most catalysts deactivate rapidly. The first observation of hydrocarbon formation from methanol in molten ZnCl2 was reported in 1880, when decomposition of methanol was described to yield hexamethylbenzene and methane.414 Significant amounts of light hydrocarbons, mostly isobutane, were formed when methanol or dimethyl ether reacted over ZnCl2 under superatmo-spheric pressure.415 More recently, bulk zinc bromide and zinc iodide were found to convert methanol to gasoline range (C4-C13) fraction (mainly 2,2,3-trimethyl-butane) at 200°C with excellent yield (>99%).416... 

Tributyltin hydride, 316 Zinc iodide, 280 From alkyl halides Lithium aluminum hydride-Ceri-um(III) chloride, 159 Palladium catalysts, 230 Sodium cyanoborohydride-Tin(II) chloride, 280 From alkyl sulfonates Lithium triethylborohydride, 153 From thiols... 

The reaction time required depends on the catalyst. Zinc iodide, zinc cyanide, and zinc bromide produce essentially complete conversion under these conditions in approximately 16.5, 28 and 30 hr, respectively, probably reflecting solubility differences. When zinc iodide is used, the distilled product is often colored because of the formation of small amounts of Iodine. 

Denmark et al. studied the effect of zinc iodide on the catalytic, enantioselective cyclopropanation of allylic alcohols with bis(iodomethyl)-zinc as the reagent and a bismethanesulfonamide as the catalyst 17]. They found significant rate enhancement and an increased enantiomeric excess of the product cyclopropane upon addition of 1 equivalent zinc iodide. Their studies and spectroscopic investigations showed that the Schlenk equilibrium appears to lie far on the left (IZnCHjI). Charette et al. used low temperature - C-NMR spectroscopy to differentiate several zinc-carbenoid species [18]. They also found evidence that in the presence of zinc iodide, bis(iodomethyl)zinc is rapidly converted to (io-domethyOzinc iodide. Solid-state structures of (halomethyl)zinc species have been described by Denmark for a bis(iodomethyl)zinc ether complex (6a) [19] and Charette for an (iodo-methyl)zinc iodide as a complex with 18-crown-6 (6b) [20] (Fig. 2). 

Protection of an enone as the dithiane derivative without destruction of an accompanying dioxane was accomplished during a synthesis of Aphidicolin [Scheme 2.90]181 by using the hw-trimethylsilyl ether of propane- 1,3-dithiol in the presence of zinc iodide as the catalyst.182 In the same vein, a synthesis of a fully functionalised B-ring system of Taxol [Scheme 2.91] included the selective thio ace tali sat ion of an aldehyde in the presence of a ketone using silver(I)-cata-lysed thioacetalisation with EtS-TMS and chlorotrimethylsilane.183... 

Protection of arylamines. Anilines react with 1 in the presence of zinc iodide as catalyst at 140° to form the adducts 2. The protecting group can be removed quantitatively with methanol containing a trace of TsOH. 

The action of metals on 1,3-dihalides is an important method of ring closure for cyclopropanes. Cyclopropane is made by the action of zinc dust at 125° on an acetamide solution of 1,3-dichloropropane. A small amount of sodium iodide is used as a catalyst, and sodium carbonate is added to regenerate iodide ions from the precipitated zinc iodide." Zinc dust in aqueous ethanol is employed in the preparation of 1,1-dialkyl-cyclopropanes from the corresponding 1,3-dibromides and spiropentane from pent aery thrityl tetrabromide." ... 

The cleavage of tetrahydrofuran and its alkylated derivatives with halogen acids is an excellent method for the preparation of, A-dihalo-alkanes.The reaction of tetrahydrofuran with the less-reactive hydrogen chloride stops at the chlorohydrin stage, whereas the reaction in the presence of zinc chloride catalyst leads to the formation of the dichloride. The crude reaction mixture containing the intermediate chlorohydrin may be treated directly with phosphorus tribromide, yielding tetramethylene chlorobromide. The preparation of dibromides can be accomplished easily with hydrogen bromide or phosphorus and bromine and diiodides, by the action of potassium iodide and orthophosphoric acid. ... 

Ketones react slowly under the same conditions but, in the presence of zinc iodide as catalyst, they also form the derivatives (2) at room temperature in excellent yields. 

The role of Z11I2 is that an equimolar quantity of the compound drives the Schlenk equilibrium from the reagent bis(iodomethyl)zinc to (iodomethyl)zinc iodide, which is the actual cyclopropanation catalyst and has high reactivity and stereoselectivity [50c,52], The structure of the active catalyst, Zn-bis(sulfonamide) complex XXIV, was characterized by NMR analysis and X-ray study of the structure of its bipyri-dyl complex 66 (Sch. 28) [53]. The Zn-bis(sulfonamide) complex XXIV aggregates in solution and functions as a divalent Lewis acid. 

The Lewis acid-base reaction of SbCls with DAST, (diethylamino)sulfur trifluoride, can be used to catalyze the conversion of sulfoxides to a-fluorothioethers (Eq. 2) [7]. Zinc iodide was originally reported to be the catalyst for this fluoro-Pummerer transformation [8a], but SbCL is markedly superior [7,8b],... 

A route to a, 8-acetylenic aldehydes is based on the fact that triethyl orthoformate in the presence of zinc iodide as catalyst reacts with a terminal acetylene with elimination of ethanol and formation of an acetal, as illustrated for the preparation of phenylpropargyl aldehyde. The reactants are heated neat with the catalyst to about 135°, and ethanol is removed by distillation (about 1 hr.). 

Furan also undergoes cycloadditions with allenes," " with benzyne" and with simpler dienophiles, like acrylonitrile and acrylate various Lewis acidic catalysts can assist" in some cases, zinc iodide is one such, hafnium tetrachloride another, and improved endo exo ratios are obtained in an ionic liquid as reaction solvent. Maleate and fumarate esters react if the addition is conducted under high pressure. This device can also be used to increase markedly the reactivity of 2-methoxyfuran and 2-acetoxyfuran towards dienophiles. At higher reaction temperatures alkynes and even electron-rich alkenes will add to furan. 3- or 5-Halo-furans react faster in these cycloadditions. ... 

A key to the success of the living cationic polymerization of vinyl ethers is the stabilization of the unstable carbocations via suitable nucleophilic counterion. There are two ways to stabilize the carbocations (1) generation of suitable nucleophilic counterion resulted from the initiator and the catalyst, and (2) addition of nucleophilic agents to the polymerization media. In the first way, Bronsted acids such as hydrogen iodide are employed as the initiators, while Lewis acids such as zinc iodide are employed as the catalysts (Scheme 11.41) [140-143],... 

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