A-Halogenated sulfones

This relative stability of cyclopropanone-zwitterion in five-membered rings can be generalized, as a similar behavior is found, for instance, in the Ram-berg-Backlund reaction of a-halogenated sulfones. (The mechanism of this reaction is known, and involves the formation of an episulfone heterocyclic analog of the cyclopropanone.) When this intermediate is formed in a strained system such as propellane 41, Paquette and coworkers suggest that it opens to a zwitterion in order to explain the formation of the substitution product 42. 

Contrary to what is observed in the Favorskii rearrangement, such a substitution product is seldom observed in the Ramberg-Backlund reaction, as cyclic a-halogenated sulfones generally give only the ring-contracted alkene under basic conditions. The sulfone which has a skeleton similar to the diene 37... 

Anthraquinone can be sulfonated, nitrated, or halogenated. Sulfonation is of the greatest technical importance because the sulfonic acid group can be readily replaced by an amino or chloro group. Sulfonation with 20—25% oleum at a temperature of 130—135°C produces predominandy anthraquinone-2-sulfonic acid [84-48-0]. By the use of a stronger oleum, disulfonic acids are produced. The second sulfonic acid substituent never enters the same ring a mixture of 2,6- and 2,7-disulfonic acids is formed (Wayne-Armstrong rule). In order to sulfonate in the 1-, 1,5-, or 1,8-positions, mercury or one of its salts must be used as a catalyst. 

The a-halogenation of sulfones is not a straightforward reaction, since (a) the carbon is at best partially positively charged due to the strong electron-withdrawing capacity of the... 

Kattenberg and coworkers54 studied the chlorination of a-lithiated sulfones with hexachloroethane. These compounds may react as nucleophiles in a nucleophilic substitution on halogen (path a, Scheme 5) or in an electron transfer reaction (path b, Scheme 5) leading to the radical anions. The absence of proof for radical intermediates (in particular, no sulfone dimers detected) is interpreted by these authors in favour of a SN substitution on X. 

Aus a-Halogen-sulfonen sind auf analoge Weisein quantitativer Ausbeute die entspre-chenden Sulfone zuganglich2 ... 

The reaction of an a-halo sulfone with a base to give an alkene is called the Ramberg-Bdcklund reaction. The reaction is quite general for a-halo sulfones with an (x hydrogen, despite the unreactive nature of a-halo sulfones in normal 8 2 reactions (p. 437). Halogen reactivity is in the order I>Br>Cl. Phase-transfer catalysis has been used. In general, mixtures of cis and trans isomers are obtained, but usually the less stable cis isomer predominates. The mechanism involves formation of an episulfone, and then elimination of SO9. There is much evidence for... 

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