1, 2-diiodoethane

Simmons-Smith reaction of cyclohexene with diiodomethane gives a single cyclopropane product, but the analogous reaction of cyclohexene with 1,1-diiodoethane gives (in low yield) a mixture of two isomeric methyl-cyclopropane products. What are the two products, and how do they differ ... 

Olefination of aldehydes with gem-dichromium reagents.1 Reduction of 1,1-diiodoethane with CrCl2 in THF provides a 1,1-dichromioethane reagent (a) that reacts with aldehydes to furnish products of ethylidenation in 80-99% yield with high (E)-selectivity (equation I). 

Problem 8.38 Show reagents and reactions needed to prepare the following compounds from the indicated starting compounds, (a) Acetylene to ethylidene iodide (1.1-diiodoethane). b) Propyne to isopropyl bromide,... 

Treatment of ketones with 1,1-dizincioethane, prepared from 1,1-diiodoethane and zinc, gives the corresponding alkenes under the action of /9-TiCl3, as shown in Scheme 16. 

Problem 8.33 Show reagents and reactions needed to prepare the following compounds from the indicated starting compounds, (a) Acetylene to ethylidene iodide (1,1-diiodoethane). (b) Propyne to isopropyl bromide, (c) 2-Butyne to racemic 2,3-dibromobutane. (d) 2-Bromobutane to trans-2-butene. (e) n-Propyl bromide to 2-hexyne. (/) 1 -Pentene to 2-pentyne. ... 

Focus on the stereochemistry of the three-membered ring. Simmons-Smith reaction of 1,1-diiodoethane with the double bond occurs with syn stereochemistry and can produce two isomers. In one of these isomers (A), the methyl group is on the same side of the three-membered ring as the cyclohexane ring carbons. In B, the methyl group is on the side of the three-membered ring opposite to the cyclohexane ring carbons. 

For example, it has been used to elaborate the chiral cyclopropanes subunits of Curacin A[60], and of the structurally fascinating FR-900848 [61] and U-106305 [62]. The chiral dioxaborolane-derived ligand was also effective to synthesize 1,2,3-substituted cyclopropanes [63]. Excellent to outstanding diastere-oselectivities and enantioselectivities were observed when a variety of allylic alcohols were treated with the reagent formed by mixing 1,1 -diiodoethane and di-ethylzinc. It was also shown that functionalized 1,1-diiodoalkanes could also be used in this reaction. 

PRACTICE PROBLEM 8.19 Treating cyclohexene with 1,1-diiodoethane and a zinc—copper couple leads to two... 

Dibromo- and 1,1,-diiodoethane, 1, l-dibromo-2,2-dimethylpropane and benzylidene bromide under several reaction conditions did not show any evidence of the formation of a geminal dimetallic species, although in all cases the starting material disappeared. Trying to capture this species immediately after its formation by an in situ reaction (as this procedure was systematically named) with cholestan-5a-3-one, resulted only in traces of the ethylenic compound being isolated. The bulk of the reaction mixture consisted of three products ... 

As is usually the case, however, specific results are dependent on the substrate in question, and the selectivity observed a case of both steric and electronic factors. For example, in their enantioselective synthesis of (-)-pinidine, Momose et al. reported a highly diastereoselective reaction employing the reagent derived from 1,1-diiodoethane and diethyl zinc. Substrate 45 was selectively converted to stereoisomer 46 in excellent yield. 

Bis-(bromomethy1)mercury converts various olefins into cyclopropanes in high yields the reactions seem less sensitive to steric effects than the Simmons-Smith procedure. Methylcyclopropanes have been obtained in far higher yields than those afforded by Simmons-Smith conditions (45-96%) from olefins and 1,1-diiodoethane in the presence of diethyl2 inc. Similarly, carbenoid (as opposed to carbene) decomposition of aryldiazomethanes in the presence of olefins, zinc halides, and lithium halides, yields cyclopropanes in 40-90% yield. ... 

These side reactions, however, can be suppressed by the addition of TMEDA. As shown in Scheme 5.16, several types of gem-dizinc compounds have been prepared. In the reaction of 1,1-diiodoethane, the addition of TMEDA proved unnecessary [18]. These dizinc species are not as stable as bis(iodozincio)methane 4. They can be stored under Ar at 25 °C for just a few hours, and gradually decompose through j8-elimination. 

Diiodoethane and Zn(Cu) react with cyclohexene to give a mixture of two isomers with the formula C8H14. (a) What are their structures, (b) Why does one isomer predominate ... 

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