Iodide, zinc

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. 

Blanchard and Simmons suggested that the stable organozinc intermediate obtained in this reaction is probably bis-(iodomethyl) zinc zinc iodide (1). 

Bis-(iodomethyl)zinc-zinc iodide, 108 17 a,20 20,21-Bismethylenedioxy- U,2 -di-hydroxypregn-4-ene-3,11 -dione, 425 17a,20 20,21-Bismethylenedioxy-3,3-ethyl-enedioxy-5a,6a-oxidopregnan-l 1-one and 5 3,6p-oxide, 3... 

Although the rationalization of the reactivity and selectivity of this particular substrate is distinct from that for chiral ketals 92-95, it still agrees with the mechanistic conclusions gained throughout the study of Simmons-Smith cyclopropa-nations. StOl, the possibility of the existence of a bimetallic transition structure similar to v (see Fig. 3.5) has not been rigorously ruled out. No real changes in the stereochemical rationale of the reaction are required upon substitution of such a bimetallic transition structure. But as will be seen later, the effect of zinc iodide on catalytic cyclopropanations is a clue to the nature of highly selective reaction pathways. A similar but unexplained effect of zinc iodide on these cyclopro-panation may provide further information on the true reactive species. 

The zinc iodide formed in a Simmons-Smith reaction can act as Lewis acid, and thereby may catalyze rearrangement reactions however interfering side-reactions are generally rare. 

More useful for synthetic purposes, however, is the combination of the zinc-copper couple with methylene iodide to generate carbene-zinc iodide complex, which undergoes addition to double bonds exclusively to form cyclopropanes (7). The base-catalyzed generation of halocarbenes from haloforms (2) also provides a general route to 1,1-dihalocyclopropanes via carbene addition, as does the nonbasic generation of dihalocarbenes from phenyl(trihalomethyl)mercury compounds. Details of these reactions are given below. 

Zink-jodid, n. zinc iodide, -kalk, m. zinc calx, zinc ash. -kastea, m. zinc case zinc tank, -kiesel, m., -kieselerz, n. (siliceous) calamine. -kitt, m. zinc cement, -kohlea-batterie, /. zinc-carbon battery, -legierung, /. zinc alloy, -losung, /. zinc solution, -mehl,... 

For a-benzyloxycyclohexaneacelaldehyde and 2-butenylstannanes, good chelation control was observed using zinc iodide and titanium(IV) chloride, but only weak synjanti selectivity. Better syn/anti selectivity was found using boron trifluoride-diethyl ether complex, but weak chelation control. Magnesium bromide gave excellent chelation control and acceptable syn/anli selectivity90. 

Diastereoselection is also observed in the catalyzed [titanium tetrachloride (TiCI4)13, trimethyl-silyltrifluoromethanesulfonate (TMSTf)l4, zinc iodide (Znl2)15] reactions of silyl ketene acetal 1 with imines 2, The ami configuration of the product 3 dominates. 

The diastereoselectivity of the zinc iodide catalyzed reaction of the azetidinone I with the trimethylsilyl enolate derivatives of the chiral 3-(l-oxopropyI)oxazolidinones 6 was considerably lower (about 60 40), although independent generation of the zinc enolate, via exchange of the lithium enolate with zinc bromide, afforded the /9-Iactam carboximide derivatives in a ratio (RIS) 80 20177. 

When we transfer energy to a constant-pressure system as hear, the enthalpy of the system increases by that amount. When energy leaves a constant-pressure system as heat, the enthalpy of the system decreases by that amount. For example, the formation of zinc iodide from its elements is an exothermic reaction that (at constant pressure) releases 208 kj of heat to the surroundings for each mole of Znl2 formed ... 

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... 

Alcohols, when treated with a thiol acid and zinc iodide, give thiol esters (R COSR). ... 

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

Other thietane derivatives have been obtained by isomerization of nitrogen-containing heterocycles. The reaction of an acyl isothiocyanate (RCONCS) with diphenyldiazomethane gave 20 and this isomerized in solution to the tetraphenyl-3-thietanone 21 <96BSB253>. Additionally, the isoxazolidine 22 was converted into 23 by the action of trimethylsilyl iodide and zinc iodide <96H1211>. 

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. "... 

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 zinc iodide complex of a 15-membered diamine diimine macrocycle has been structurally... 

See Sulfuric acid Zinc iodide See other METAL HALIDES... 

Asymmetric 1,3-dipolar cycloaddition of cyclic nitrones to crotonic acid derivatives bearing chiral auxiliaries in the presence of zinc iodide gives bicyclic isoxazolidines with high stereoselectivity (Eq. 8.51). The products are good precursors of (3-amino acids such as (+)sedridine.73 Many papers concerning 1,3-dipolar cycloaddition of nitrones to chiral alkenes have been reported, and they are well documented (see Ref. 63). 

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). 

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