Favorskii, quasi rearrangement

Kraus and co-workers utilized the quasi-Favorskii rearrangement of a bicyclic bridgehead bromide as the key step in their formal total synthesis of ep/-modhephene. The required bicyclo[3.3.1]nonenone bridgehead bromide precursor was prepared by a Robinson annulation reaction between 3-bromo-2-oxocyclohexanecarboxylate and MVK. Upon treatment with lithiated dimethyl methylphosphonate, the bicyclic bromo ketone underwent a facile quasi-Favorskii rearrangement to afford the key intermediate bicyclo[3.3.0]octane derivative. 

A formal total synthesis of racemic spatol was accomplished by M. Harmata et al. using an intermolecular [4+3] cycloaddition of a haiogenated cyclopentenyl cation with cyclopentadiene followed by a quasi-Favorskii rearrangement as the key steps.  

Harmata and co-workers successfully synthesized racemic sterpurene using an intermolecular [4+3] cycloaddition to prepare the key quasi-Favorskii rearrangement precursor. The tricyclic bridgehead a-bromo ketone was first treated with LAH at 0 °C to get the corresponding secondary alcohol. Treatment of this alcohol with KH triggered the expected ring-contraction to afford the 5-6-4 fused tricyclic aldehyde, which was then reduced to the primary alcohol with LAH. 

If there are no enolizable hydrogens present, the classical Favorskii leanangement is not possible. Instead, a semi-benzylic mechanism can lead to a leanangement referred to as quasi-Favorskii. 

Filipski, K.J. Pfefferkom, J. A. Favorskii Rearrangement. In Name Reactions for Homologations-Part II, Li, J. J., Ed. Wiley Hoboken, NJ, 2009, pp 438-452. (Review). 

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This is usually called the quasi-Favorskii rearrangement. An example is found in the... 

The quasi-Favorskii rearrangement obviously cannot take place by the cyciopropanone mechanism. The mechanism that is generally accepted (called the semi-... 

The mechanism discussed is in accord with all the facts when the halo ketone contains an a hydrogen on the other side of the carbonyl group. However, ketones that do not have a hydrogen there also rearrange to give the same type of product. This is usually called the quasi-Favorskii rearrangement. An example is found in the preparation of Demerol ... 

Quasi-Favorskii rearrangement Skeletal rearrangement of bicyclic a-halo ketones in which the halogen is located at the bridgehead position to afford carboxylic acids or carboxylic acid derivatives. 370... 

Harmata, M., Bohnert, G., Kurti, L., Barnes, C. L. Intramolecular 4+3 cycloadditions. A cyclohexenyl cation, its halogenated congener and a quasi-Favorskii rearrangement. Tetrahedron Lett. 2002,43, 2347-2349. 

In order to distinguish between a mechanism proceeding via a symmetrical cyclopropanone intermediate (Favorskii reaction) and a mechanism closely related to the benzilic acid rearrangement and called semibenzilic (or quasi-Favorskii) rearrangement, the ring contraction of 2-bromocyclobutanone was studied in deuterium oxide using sodium carbonate as base (50 C) or in boiling deuterium oxide only. 

Butyllithium Carboxylic acid amides from a-halogenoketones Quasi-Favorskii rearrangement... 

Scheme 7.12 Haller-Bauer and other side reactions in an attempted quasi-Favorskii rearrangement.

Schemes 7.16 t4+3i-Cycloaddition of a chlorinated cyclopentenyl oxyallylic cation. Figure 7.] 7 r4+3i-Cycloaddition of a brominated cyclopentenyl oxyallylic cation. Scheme 7.1R Quasi-Favorskii rearrangements from r4+3Vcycloadducts.

Scheme 7.19 Control over quasi-Favorskii rearrangements.

Scheme 7.21 Intramolecular t4+Si-cycloaddition and subsequent quasi-Favorskii rearrangement.

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