Alkenes with iodomethylzinc iodide

Simmons-Smith reaction (Section 14.12) Reaction of an alkene with iodomethylzinc iodide to form a cyclopropane derivative. 

What alkenes would you choose as starting materials in order to prepare each of the following cyclopropane derivatives by reaction with iodomethylzinc iodide ... 

What makes iodomethylzinc iodide such a useful reagent is that it reacts with alkenes to give cyclopropanes. 

Cyclopropanation with Halomethylzinc Reagents. A very effective means for conversion of alkenes to cyclopropanes by transfer of a CH2 unit involves reaction with methylene iodide and a zinc-copper couple, referred to as the Simmons-Smith reagent.169 The reactive species is iodomethylzinc iodide.170 The transfer of methylene occurs stereospecifically. Free CH2 is not an intermediate. Entries 1 to 3 in Scheme 10.9 are typical examples. 

Cyclopropanation of alkenes with the Simmons-Smith reagent bears some similarity to epoxidation. Both reactions are stereospecific cycloadditions, and iodomethylzinc iodide behaves, like peroxy acids, as a weak electrophile. Both cycloadditions take place faster with more highly substituted double bonds than less substituted ones, but are sensitive to steric hindrance in the alkene. These similarities are reflected in the mechanisms proposed for the two reactions shown in Mechanism 14.2. Both are believed to be concerted. 

The transition state for the reaction of an alkene with the Simmons—Smith reagent results from a concerted transfer of a methylene unit from the iodomethylzinc iodide. 

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