Halogen with rearrangement

An interesting analog of the Favorskii rearrangement treats a ketone such as 4-/ r/-butylcyclohexanone, without an oc-halogen with T1(N03)3 to give 3-tert-butylcyclopentane-1 -carboxylic acid. ... 

Chemical reactions are used to modify existing polymers, often for specialty applications. Although of considerable importance for plastics, very few polymer reactions (aside from crosslinking) are important for elastomers. Chlorination and bromination of Butyl rubber to the extent of about one halogen atom per isoprene unit yields elastomers which are more easily crosslinked than Butyl rubber. Substitution occurs with rearrangement to yield an allylic halide structure... 

Cavell and Dobbie (214-216) have suggested that halogen transfer rearrangements in trifluoromethylphosphines arise from interactions of nonbonding fluorine p orbitals with vacant d orbitals on phosphorus. Such an explanation is consistent with observations for the Groups IV and V pentafluorophenyl derivatives, exclusive of carbon and nitrogen, and similarly fits the behavior of boron with its vacant p orbital. 

The di-iodides (81), formed from cyclopropenes by addition of iodine with rearrangement also eliminate halogen on reaction with methyllithium, providing a simple route to l-vinyl-2-alkylbicyclo[l. 1. OJbutanes180. 

However, at low temperatures the reverse reaction is very slow and the forward reaction is practically irreversible Sulfur trioxide reacts much more rapidly than sulfuric acid with benzene it is nearly instantaneous. Sulfones are often side products. When sulfonation is carried out on a benzene ring containing four or five alkyl and/or halogen groups, rearrangements usually occur (see 11-36). 

A similar competition between the substitution of the allylic halogen and rearrangement with loss of halogen leading to bicyclic compounds, i.e. 6-alkyl-6-pyrrolidinobicyclo[3.1.0]hexanes was observed upon treatment of a-halogenated cyclic enamines with organometallic reagents (Mg, Li, Cu, hydrides) (Table 2). ° ... 

Carbene complexes of the type 28 with X being a halogen spontaneously rearrange to the dialkylaminocarbyne complex 29 under elimination of... 

Ammonolysis of aromatic halides, however, may lead to unexpected products. For example, Gilman and Martin report that aryl ethers, thio ethers, and sulfones with ortho-halogen substituents rearrange to metarsubstituted anilines when treated with sodamide in liquid NH3. 

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