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The Buchner ring expansion is a two-step organic C-C bond forming reaction used to access 7-membered rings. The first step involves formation of a carbene from ethyl diazoacetate , which cyclopropanates an aromatic ring.
Definitive mechanistic studies of rhodium-catalyzed cyclopropanation are lacking. However, the mechanism has been rationalized based on product distribution and stereoselectivity. [4] Attack of the diazo compound on the metal center generates a zwitterionic metal alkyl complex, which expels nitrogen gas to afford a metal carbene intermediate.
The strategy can start with a Simmons-Smith-like cyclopropanation of a cyclic alkene. [3] A related cyclopropane-based ring expansion is the Buchner ring expansion. The Buchner ring expansion is used to convert arenes to cycloheptatrienes. The Buchner ring expansion is encouraged to open to the desired product by placing electron withdrawing ...
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]
The key step in one synthesis of barbaralone is the selective intramolecular cyclopropanation of a cycloheptatriene. [10] (3) α,β-Cyclopropyl ketones may act as masked α,β-unsaturated ketones. In one example, intramolecular participation of an aryl group leads to the formation of a polycyclic ring system with complete diastereoselectivity ...
The Buchner–Curtius–Schlotterbeck reaction is the reaction of aldehydes or ketones with aliphatic diazoalkanes to form homologated ketones. [1] It was first described by Eduard Buchner and Theodor Curtius in 1885 [ 2 ] and later by Fritz Schlotterbeck in 1907. [ 3 ]
Examples of intramolecular reactions with a tethered alkyne [11] and intermolecular reactions with a nontethered alkyne [12] both exist with use of a nickel or rhodium catalyst. With the six-membered alkyl metal enolate intermediate, dimerization [ 13 ] [ 14 ] or reaction with an added alpha-beta unsaturated ketone [ 15 ] yields a 1,3 ...
An example of the former, cyclopropyl cyanide is prepared by the reaction of 4-chlorobutyronitrile with a strong base. [1] Phenylcyclopropane is produced analogously from the 1,3-dibromide. [2] A second major route to cyclopropanes entails addition of methylene (or its substituted derivatives) to an alkene, a process called cyclopropanation. [3]