Simmons-Smith reaction of cyclohexene with diiodomethane...

Name: Problem 50, Chapter 8: Organic Chemistry
Uploaded: 2020-09-26T03:43:00-08:00
Duration: 4 min 29 s
Channel: Anupa Sharad Medhekar
Description: 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 methylcyclopropane products. What are the two products, and how do they differ?

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 methylcyclopropane products. What are the two products, and how do they differ?

Key Concepts

Simmons-Smith Reaction

The Simmons-Smith reaction is a cyclopropanation method that converts alkenes into cyclopropane rings through the use of a zinc carbenoid intermediate. Typically generated from a dihalomethane (like diiodomethane) and a zinc reagent (such as diethylzinc), the process is known for its mild reaction conditions and high stereospecificity, usually transferring the geometry of the starting alkene into the new cyclopropane ring.

Carbenoid Intermediates

Carbenoid intermediates are reactive species that behave similarly to carbenes but are stabilized through bonding with a metal center, such as zinc. In the Simmons-Smith reaction, the carbenoid formed from the dihalomethane interacts with the alkene in a concerted process, leading to cyclopropane formation while often retaining the stereochemical arrangement of substituents from the original double bond.

Stereospecificity in Cyclopropanation

A key feature of the Simmons-Smith reaction is its typically stereospecific nature, meaning that the configuration of the alkene is directly translated into the cyclopropane product. However, when the carbenoid carries additional substituents, the stereochemical outcome can become more complex, sometimes resulting in multiple stereoisomeric products due to alternative approaches or orientations during the cyclopropanation step.

Stereochemical Outcomes in Substituted Cyclopropanes

When using substituted dihalomethanes to form carbenoids, steric and electronic effects can lead to the formation of different stereoisomers of the cyclopropane product. In such cases, the addition of a substituted carbenoid to an alkene can give rise to isomeric cyclopropanes that differ in the spatial orientation of the substituent (for example, differing as cis versus trans or endo versus exo configurations relative to a cyclic framework), highlighting the role of steric hindrance and reaction pathways in determining the final product stereochemistry.

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