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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. The ring expansion occurs in the second step, with an electrocyclic reaction opening the cyclopropane ring to form the 7 ...
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 ]
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.
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.
Cyclopropane is the cycloalkane with the molecular formula (CH 2) 3, consisting of three methylene groups (CH 2) linked to each other to form a triangular ring.The small size of the ring creates substantial ring strain in the structure.
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.
Diazoketones containing pendant double bonds undergo cyclopropanation in the presence of copper. 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.
Beta-carbon elimination to form an alkene from the other carbon-rhodium bond leads to a rhodacyclohexanone intermediate with an exocyclic double bond. Reductive elimination of the two carbon-rhodium bonds followed by isomerization of the exocyclic double bond leads to the desired beta-substituted cyclopentenone product. This reaction was ...