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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.
Initial steps in the Buchner–Curtius–Schlotterbeck reaction mechanism. The reaction is then completed either by the reformation of the carbonyl through an 1,2-rearrangement or by the formation of the epoxide. There are two possible carbonyl products: one formed by migration of R 1 (4) and the other by migration of R 2 (5). The relative ...
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.
In the case of arenes, the cyclopropanation product undergoes further electrocyclic ring opening to give cycloheptatriene products (Buchner ring expansion). [2] Alkenes undergo both C=C methylenation and C–H methylenation insertion to give a mixture of cyclopropanation and homologation products.
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Eduard Buchner (German: [ˈeːduaʁt ˈbuːxnɐ] ⓘ; 20 May 1860 – 13 August 1917) was a German chemist and zymologist, awarded the 1907 Nobel Prize in Chemistry for his work on fermentation. [ 1 ]
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The Dieckmann method is practical only for 5- to 8-membered rings (with modest yields for 7- and 8-membered). The Thorpe method is more easily modified via high dilution (e.g., 0.001 M in benzene/ether) to enable the synthesis of large rings, but 4-membered and 9- to 13-membered rings are still not accessible.