Matches in DBpedia 2016-04 for { ?s ?p "The Simmons–Smith reaction is an organic cheletropic reaction involving an organozinc carbenoid that reacts with an alkene (or alkyne) to form a cyclopropane. It is named after Howard Ensign Simmons, Jr. and Ronald D. Smith. It uses a methylene free radical intermediate that is delivered to both carbons of the alkene simultaneously, therefore the configuration of the double bond is preserved in the product and the reaction is stereospecific.Simmons–Smith reaction mechanismThus, cyclohexene, diiodomethane, and a zinc-copper couple (as iodomethylzinc iodide, ICH2ZnI) yield norcarane (bicyclo[4.1.0]heptane).An example of the Simmons–Smith reactionThe Simmons–Smith reaction is generally preferred over other methods of cyclopropanation, however it can be expensive due to the high cost of diiodomethane. Modifications involving cheaper alternatives have been developed, such as dibromomethane or diazomethane and zinc iodide. The reactivity of the system can also be increased by exchanging the zinc‑copper couple for diethylzinc, however as this reagent is pyrophoric it must be handled carefully.The Simmons–Smith reaction is generally subject to steric effects, and thus cyclopropanation usually takes place on the less hindered face. However, when a hydroxy substituent is present in the substrate in proximity to the double bond, the zinc coordinates with the hydroxy substituent, directing cyclopropanation cis to the hydroxyl group (which may not correspond to cyclopropanation of the sterically most accessible face of the double bond): An interactive 3D model of this reaction can be seen here (java required).An example of a stereoselective Simmons–Smith reactionThe Simmons–Smith reagent, namely diiodomethane and diethylzinc, can react with allylic thioethers to generate sulfur ylides, which can subsequently undergo a 2,3-sigmatropic rearrangement, and will not cyclopropanate an alkene in the same molecule unless excess Simmons–Smith reagent is used:An example of the use of the Simmons–Smith reagent to generate a sulfur ylide↑ ↑ ↑ ↑ ↑ ↑ ↑ ↑ ↑ ↑ ↑ ↑ ↑ ↑"@en }
Showing triples 1 to 2 of
2
with 100 triples per page.
- Simmons–Smith_reaction abstract "The Simmons–Smith reaction is an organic cheletropic reaction involving an organozinc carbenoid that reacts with an alkene (or alkyne) to form a cyclopropane. It is named after Howard Ensign Simmons, Jr. and Ronald D. Smith. It uses a methylene free radical intermediate that is delivered to both carbons of the alkene simultaneously, therefore the configuration of the double bond is preserved in the product and the reaction is stereospecific.Simmons–Smith reaction mechanismThus, cyclohexene, diiodomethane, and a zinc-copper couple (as iodomethylzinc iodide, ICH2ZnI) yield norcarane (bicyclo[4.1.0]heptane).An example of the Simmons–Smith reactionThe Simmons–Smith reaction is generally preferred over other methods of cyclopropanation, however it can be expensive due to the high cost of diiodomethane. Modifications involving cheaper alternatives have been developed, such as dibromomethane or diazomethane and zinc iodide. The reactivity of the system can also be increased by exchanging the zinc‑copper couple for diethylzinc, however as this reagent is pyrophoric it must be handled carefully.The Simmons–Smith reaction is generally subject to steric effects, and thus cyclopropanation usually takes place on the less hindered face. However, when a hydroxy substituent is present in the substrate in proximity to the double bond, the zinc coordinates with the hydroxy substituent, directing cyclopropanation cis to the hydroxyl group (which may not correspond to cyclopropanation of the sterically most accessible face of the double bond): An interactive 3D model of this reaction can be seen here (java required).An example of a stereoselective Simmons–Smith reactionThe Simmons–Smith reagent, namely diiodomethane and diethylzinc, can react with allylic thioethers to generate sulfur ylides, which can subsequently undergo a 2,3-sigmatropic rearrangement, and will not cyclopropanate an alkene in the same molecule unless excess Simmons–Smith reagent is used:An example of the use of the Simmons–Smith reagent to generate a sulfur ylide↑ ↑ ↑ ↑ ↑ ↑ ↑ ↑ ↑ ↑ ↑ ↑ ↑ ↑".
- Q903776 abstract "The Simmons–Smith reaction is an organic cheletropic reaction involving an organozinc carbenoid that reacts with an alkene (or alkyne) to form a cyclopropane. It is named after Howard Ensign Simmons, Jr. and Ronald D. Smith. It uses a methylene free radical intermediate that is delivered to both carbons of the alkene simultaneously, therefore the configuration of the double bond is preserved in the product and the reaction is stereospecific.Simmons–Smith reaction mechanismThus, cyclohexene, diiodomethane, and a zinc-copper couple (as iodomethylzinc iodide, ICH2ZnI) yield norcarane (bicyclo[4.1.0]heptane).An example of the Simmons–Smith reactionThe Simmons–Smith reaction is generally preferred over other methods of cyclopropanation, however it can be expensive due to the high cost of diiodomethane. Modifications involving cheaper alternatives have been developed, such as dibromomethane or diazomethane and zinc iodide. The reactivity of the system can also be increased by exchanging the zinc‑copper couple for diethylzinc, however as this reagent is pyrophoric it must be handled carefully.The Simmons–Smith reaction is generally subject to steric effects, and thus cyclopropanation usually takes place on the less hindered face. However, when a hydroxy substituent is present in the substrate in proximity to the double bond, the zinc coordinates with the hydroxy substituent, directing cyclopropanation cis to the hydroxyl group (which may not correspond to cyclopropanation of the sterically most accessible face of the double bond): An interactive 3D model of this reaction can be seen here (java required).An example of a stereoselective Simmons–Smith reactionThe Simmons–Smith reagent, namely diiodomethane and diethylzinc, can react with allylic thioethers to generate sulfur ylides, which can subsequently undergo a 2,3-sigmatropic rearrangement, and will not cyclopropanate an alkene in the same molecule unless excess Simmons–Smith reagent is used:An example of the use of the Simmons–Smith reagent to generate a sulfur ylide↑ ↑ ↑ ↑ ↑ ↑ ↑ ↑ ↑ ↑ ↑ ↑ ↑ ↑".