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Cyclopropanation is also stereospecific as the addition of carbene and carbenoids to alkenes is a form of a cheletropic reaction, with the addition taking place in a syn manner. For example, dibromocarbene and cis-2-butene yield cis-2,3-dimethyl-1,1-dibromocyclopropane, whereas the trans isomer exclusively yields the trans cyclopropane. [16]
Although asymmetric cyclopropanation methods based on diazo compounds (the Metal-catalyzed cyclopropanations) exist since 1966, the asymmetric Simmons–Smith reaction was introduced in 1992 [14] with a reaction of cinnamyl alcohol with diethylzinc, diiodomethane and a chiral disulfonamide in dichloromethane:
Cyclopropanation of olefins with diazocarbonyl compounds is commonly accomplished using rhodium carboxylate complexes, although copper was originally used. [11] The scope of the olefin is generally quite broad—electron-rich, [ 12 ] neutral, [ 13 ] and electron-poor [ 14 ] olefins have all been cyclopropanated efficiently using rhodium-based ...
A second major route to cyclopropanes entails addition of methylene (or its substituted derivatives) to an alkene, a process called cyclopropanation. [3] Substituted cyclopropanes undergo the reactions associated with the cyclopropyl ring or the substituents. Vinylcyclopropanes are a special case as they undergo vinylcyclopropane rearrangement.
[3] [10] Many electron-withdrawing groups have been shown promote the cyclopropanation including ketones, esters, amides (the example below involves a Weinreb amide), sulfones, nitro groups, phosphonates, isocyanides and even some electron deficient heterocycles. [15] Cyclopropanation with the Johnson–Corey–Chaykovsky reaction
The advent of transition metal catalyzed reagents provides alternative stereospecific methods for cyclopropanation. The choices for metals include Cu, Rh and Ru with a variety of ligands. [ 13 ] The use of rhodium catalysts in the Buchner reaction for carbene generation reduces the number of products by producing predominantly the kinetic ...
The Kulinkovich reaction describes the organic synthesis of substituted cyclopropanols through reaction of esters with dialkyldialkoxytitanium reagents, which are generated in situ from Grignard reagents containing a hydrogen in beta-position and titanium(IV) alkoxides such as titanium isopropoxide. [1]
Structure of the platinacyclobutane PtC 3 H 6 (bipy) derived from activation of cyclopropane.. In organometallic chemistry, the activation of cyclopropanes by transition metals is a research theme with implications for organic synthesis and homogeneous catalysis. [1]