Base-catalysed halogen dance

Halogen dance The rearrangement of polyhalogenobenzenes catalysed by very strong bases, which proceeds via an aryl carbanion intermediate (i.e. an SE1 mechanism). 

There are two complications that can arise in the formation and the use of lithiated thiophenes the occurence of a Base Catalysed Halogen Dance ,and the isomerisation or ring opening of 3-lithiated thiophenes. As an example of the first of these, and one in which the phenomenon is put to good use, consider the transformation of 2-bromothiophene into 3-bromothiophene by reaction with sodamide in ammonia. The final result is governed, in a set of equilibrations, by the stability of the hnal anion the system settles to an anion in which the charge is both adjacent to halogen and at an a-position. 

The base-catalysed halogen dance, and other reactions of aryl halides , Bunnett, J. F, Acc. Chem. Res., 1972, 5, 139. 

Scheme 71 The mechanism of base-catalysed halogen dance (BCHD) reaction [112]...

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See also in sourсe #XX -- [ ]

See also in sourсe #XX -- [ ]

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