Diiodomethane-Zinc-copper couple

Diethylzinc-Titanium(IV) chloride, 21 Diiodomethane-Diethylzinc, 276 Diiodomethane-Zinc-copper couple, 275... 

The classical Simmons-Smith reagent was used to cyclopropanate a double bond in the presence of a triple bond in the synthesis of racemic 11,12-cyclopropyl analogs of hepoxilins Aj and ( )-Undec-2-en-5-ynol (4) was treated with diiodomethane/zinc-copper couple in anhydrous diethyl ether to afford the intermediate racemic (lS, 2S )-l-hydroxymethyl-2-... 

Table 2. Reaction of (S,S )-Hydrobenzoin Acetals with Diiodomethane/Zinc-Copper Couple ...

Conia and his co-workers ) modified the Simmons-Smith reaction ) by using enol ether plus predominantly diiodomethane/zinc-silver couple instead of the common known diiodomethane/zinc-copper couple ). This method is an excellent access to cyclopropanols and related compounds ) (Scheme 29). Furthermore,... 

Diiodomethane/zinc-copper couple and diiodomethane-triisobutylaluminum complex are particularly valuable reagents for the insertion of a methylene group into olefmic double... 

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... 

Without question, the most powerful method for cyclopropane formation by methylene transfer is the well-known Simmons-Smith reaction [6]. In 1958, Simmons and Smith reported that the action of a zinc-copper couple on diiodomethane generates a species that can transform a wide variety of alkenes into the corresponding cyclopropanes (Scheme 3.3) [7]. 

By reaction of zinc-copper couple with diiodomethane 2 an organozinc species 4 is formed, similar to a Grignard reagent. Its structure cannot be fully described by a single structural formula. The actual structure depends on the reaction conditions—e.g. the solvent used this corresponds to the Schlenk equilibrium as it is observed with the Grignard reaction ... 

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. "... 

The direct reaction of zinc metal with organic iodides dates back to the work of Frankland(67). Several modifications have been suggested since that time to increase the reactivity of the metal. The majority of these modifications have employed zinc-copper couples(68-72), sodium-zinc alloys(73), or zinc-silver couples(77). Some recent work has indicated that certain zinc-copper couples will react with alkyl bromides to give modest yields of dialkylzinc compounds(74,73). However, all attempts to react zinc with aryl iodides or bromides have met with failure. The primary use of zinc couples has been in the Simmons-Smith reaction. This reaction has been primarily used with diiodomethane as 1,1-dibromides or longer chain diiodides have proven to be too unneactive even with the most reactive zinc couples. 

A convenient method for the conversion of aldehydes (RCHO) to alkenes (RCH = CHj), knovm as methylenation, involves the reaction of a zinc/copper couple with diiodomethane in the presence of the carbonyl compound dissolved in tetrahy-drofuran. The reaction first generates an organometallic intermediate (ICH2ZnI) which then reacts with the carbonyl compound. The conversion of benzaldehyde to styrene using this conventional methodology required a reaction time of 6 h at 40 °C. When the reaction was sonicated however comparable yields of around 70%... 

The Simmons-Smith reaction " and its variants are widely used for the stereospecific synthesis of cyclopropane compounds. The methodology involves the use of copper-treated zinc metal (the zinc-copper couple) with diiodomethane to add methylene to a carbon-carbon double bond. Alternative use of diazomethane in catalytic reactions does not offer the same synthetic advantages and is usually avoided because of safety considerations. As significant as is the Simmons-Smith reaction for cyclopropane formation, its employment for organic synthesis was markedly advanced by the discovery that allylic and homoallylic hydroxyl groups accelerate and exert stereochemical control over cyclopropanation of alkenes (e.g, Eq. 21), and this acceleration has been explained by a transition state model... 

A branched-chain iodo sugar derivative, l,5-anhydro-4,6-0-benzyl-idene-2,3-dideoxy-3-C-(iodomethyl)-D-rifoo-hex-l-enitol [4,6-O-ben-zylidene-3-deoxy-3-C-(iodomethyl)-D-allal] (200), is one of the products formed on treatment of methyl 4,6-0-benzylidene-2,3-dideoxy-a-D-en/thro-hex-2-enopyranoside (77) with the Simmons-Smith reagent (diiodomethane and zinc-copper couple).123,212 Compound 200 displays high solvolytic reactivity, an observation that has been rationalized by supposing the formation of the highly stabilized carbonium ion213 (201). Thus, under conditions wherein methyl 2,3,4-tri-0-acetyl-6-deoxy-6-iodo-a-D-glucopyranoside required more than 24 hours to react appreciably with an excess of silver nitrate in 50% aqueous p-dioxane buffered with silver carbonate, the iodide 200 was hydrolyzed completely in less than 1 minute the product of hydrolysis of 200 is the cyclopropyl aldehyde 202. Methanolysis of... 

Not only a zinc-copper couple, but also a zinc-lead couple forms a gem-dimetal species from diiodomethane, according to the 1975 Nysted patent5. He also insisted that treatment of dibromethane with a zinc-lead couple in THF at 80 °C forms a characteristic gem-dizinc species 1 (equation 3). However, there was no further evidence concerning the structure except H NMR data, which was not enough for the complete structural determination. The obtained compound was definitely a gem-dizinc species, but the written structure 1 was not fully characterized. The white solid 1 is obtained as a dispersion in THF, and does not dissolve in DMF and DMI (l,3-dimethyl-2-imidazolidinone). This THF dispersion is commercially available from Aldrich Co. as Nysted reagent. Nysted also showed that this dizinc compound is effective for the methylenation of a-hydroxy ketone moiety in steroid derivatives5. 

A cyclopropanation of an alkene using the carbenoid reagent generated from diiodomethane and the zinc-copper couple, (p. 358)... 

Diiodomethane, CH2I2 Reacts with alkenes in the presence of zinc-copper couple to yield cyclopropanes (Simmons-Smith reaction Section 7.6). 

Nonhalogenated cyclopropanes can be prepared by the reaction of an alkene with diiodomethane, CH2I2, in the presenee of a eopper-aetivated zinc reagent called zinc-copper couple [Zn(Cu)]. This proeess, the Sinunons-Smith reaction, is named for H. E. Simmons and R. D. Smith. DuPont ehemists who diseovered the reaction in 1959. 

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