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Carbanions Favorskii rearrangement

A common intermediate is required in this Favorskii rearrangement to set the same product. Removal of an aH by OH- is followed by an SN2 displacement of Cl- to give a cyclopropanone ring. Ring opening occurs to give the more stable benzylic carbanion. [Pg.217]

The generally accepted mechanism for the Favorskii rearrangement involves the formation of reactive cyclopropanone intermediate C. Base abstracts the a-hydrogen from A to give the carbanion B, which undergoes intramolecular Sn2 displacement of the halide ion. The resulting cyclopropanone intermediate C is opened under the reaction conditions to give the more stable carbanion D, which takes proton from solvent to furnish the final product, an ester E (Scheme 2.25). [Pg.69]

The canonical formulation of the mechanism of the Favorskii rearrangement involves initial deprotonation of the a-carbon to generate an enolate, intramolecular displacement of the leaving group on the a -carbon by the enolate to generate a cyclopropanone, addition of a nucleophile to the cyclopropanone ketone followed by elimination to generate the more stable of two possible carbanions, and protonation to yield the rearranged carboxylic acid derivative. [Pg.111]

Since the occurrence of a cyclopropanone mechanism was now considered to be beyond doubt, the studies carried out on the Favorskii rearrangement were directed toward a better understanding of the process leading to this cyclopropanone. The first step of the symmetrical mechanism leads to the formation of a carbanion enolate (Scheme 2) by an a hydrogen abstraction with... [Pg.532]

Another common and useful rearrangement is the Favorskii rearrangement, which involves a carbanion intermediate. An example is shown in Eq. 11.60. It involves the base-induced conversion of an a-halo carbonyl to a carboxylate. If the starting material is a cyclic ketone, a ring contraction results, and this is one of the most useful applications of the Favorskii rearrangement. [Pg.682]

The base-catalysed rearrangements of cz-halo ketones are classical examples of the reactions of ambident enolate anions in solution. The extent of each of the two reactions shown in Equations [11] and [12] is principally a function of the type of solvent used. A protic solvent solvates more strongly at the oxygen centre of the ambident anion and thus reaction proceeds through the carbanion centre to yield the Favorskii species as the major product (Eqn [11]). In marked contrast, the Favorskii rearrangement does not occur in the gas phase. Here,... [Pg.304]

The stereoselectivity of the Favorskii rearrangement described above can be explained by the mechanism of the reaction, as shown in Scheme 18.4. The ring opening of the cyclopropane ring of 16 could a priori occur by two possible routes (a or b). Less substituted carbanions are more stable. However, in such a case, the more substituted carbanion 18 is favored (path b) because of the presence of the electron-withdrawing oxygen substituent. [Pg.502]

A reaction related to the pure carbanion rearrangement, but one that eventually involves an external displacing agent as well, is the Favorskii reaction. It has been shown with the aid of isotopic tracers that the mechanism is 429... [Pg.230]

Similarly, carbanions from 1,3-dicarbonyl compounds can act as nucleophiles [153]. In a somewhat related reaction, enamines of cyclohexanone or cycloheptanone are oxidized in an iodide-mediated indirect electrochemical process leading to a Favorskii-type rearrangement. Thus, bicyclo[(n — 1).1.0] systems containing a nucleophile like a cyano or a methoxy function are formed [Eq. (27)] [154]. [Pg.565]


See other pages where Carbanions Favorskii rearrangement is mentioned: [Pg.103]    [Pg.108]    [Pg.126]    [Pg.223]    [Pg.164]    [Pg.164]    [Pg.159]    [Pg.3]    [Pg.150]    [Pg.684]    [Pg.87]    [Pg.1026]    [Pg.110]    [Pg.532]    [Pg.579]    [Pg.552]    [Pg.682]    [Pg.682]    [Pg.869]    [Pg.843]   
See also in sourсe #XX -- [ Pg.107 ]

See also in sourсe #XX -- [ Pg.69 , Pg.70 ]




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