Why is carbene electrophilic

More by Li Wu. More by Ping Lu. More by Yanguang Wang. Cite this: J. Article Views Altmetric -. Citations Supporting Information. Cited By. This article is cited by 10 publications. Preparation of 4-Diazoisoquinolinones via Dimroth Rearrangement and Their Extension to 4-Aryltetrahydroisoquinolinones.

Organic Letters , 22 1 , Recent advances in the synthesis of indole embedded heterocycles with 3-diazoindolinimines. Organic Chemistry Frontiers , 8 9 , Synthesis , 53 04 , Thus, Ea is lowest for the addition of the carbene to the highly electrophilic chloroacrylonitrile 3.

Organic Lett. Difluorodiazirine was generated by the reaction of 2,4-dinitrophenoxyfluoro-diazirine with lithium fluoride and crown-5 in HMPA. The rate constants were measured for additions to these alkenes and compared to those determined previously for additions of CCl2 and CClF. Computational studies are in progress aimed at understanding these unexpected results.

Latent Nucleophilicity of Dichlorocarbene. Dichlorocarbene CCl2 is generally regarded as an electrophilic carbene that preferentialy adds to electron-rich nucleophilic alkenes. However, a singlet carbene like CCl2 is inherently both an electrophile and a nucleophile. Triplet carbenes do not retain stereochemistry in the product molecule.

Addition reactions are commonly very fast and exothermic. The slow step in most instances is generation of carbene. A well-known reagent employed for alkene-to-cyclopropane reactions is Simmons-Smith reagent.

This reagent is a system of copper, zinc, and iodine, where the active reagent is believed to be iodomethylzinc iodide. Reagent is complexed by hydroxy groups such that addition commonly happens syn to such group. Insertions are another common type of carbene reactions. The carbene basically interposes itself into an existing bond. The order of preference is commonly: 1.

X—H bonds where X is not carbon 2. C—H bond 3. C—C bond. Insertions may or may not occur in single step. Intramolecular insertion reactions present new synthetic solutions. Generally, rigid structures favor such insertions to happen. When an intramolecular insertion is possible, no intermolecular insertions are seen.

In flexible structures, five-membered ring formation is preferred to six-membered ring formation. Both inter- and intramolecular insertions are amendable to asymmetric induction by choosing chiral ligands on metal centers. Alkylidene carbenes are alluring in that they offer formation of cyclopentene moieties. To generate an alkylidene carbene a ketone can be exposed to trimethylsilyl diazomethane. Carbenes and carbenoid precursors can undergo dimerization reactions to form alkenes. While this is often an unwanted side reaction, it can be employed as a synthetic tool and a direct metal carbene dimerization has been used in the synthesis of polyalkynylethenes.

Persistent carbenes exist in equilibrium with their respective dimers. This is known as the Wanzlick equilibrium. In organometallic species, metal complexes with the formulae L n MCRR' are often described as carbene complexes.

Such species do not however react like free carbenes and are rarely generated from carbene precursors, except for the persistent carbenes. The transition metal carbene complexes can be classified according to their reactivity, with the first two classes being the most clearly defined:. Singlet and triplet carbenes The two classes of carbenes are singlet and triplet carbenes. Figure 1: Image used with permission from Wikipedia.

Reactivity Carbene addition to alkenes. Cyclopropanation Carbenes add to double bonds to form cyclopropanes. Carbene cyclopropanation. C—H insertion. Carbene intramolecular reaction. Carbene intermolecular reaction. Alkylidene carbene. Carbene dimerization Carbenes and carbenoid precursors can undergo dimerization reactions to form alkenes. Figure : Wanzlick equilibrium. Carbene ligands in organometallic chemistry In organometallic species, metal complexes with the formulae L n MCRR' are often described as carbene complexes.