Sulfur dichloride, reaction with aromatic compounds

A modification of the reaction of a-aminoacetonitrile (37a) has been developed which leads to 3,4-dichloro-l,2,6-thiafiiazole (39) in over 80% yield. The action of commercial sulfur dichloride on 37a produces a 1-1 mixture of 3-chloro- and 3,4-dichloro-l,2,5-thiadiazole, (38 and 39). However, if excess chlorine is added to the reaction mixture the dichloro compound forms exclusively in 82 % yield. It was shown that the dichloro compound does not form via chlorination of 3-chloro-1,2,5-thiadiazole. Therefore, either chlorination takes place on one of the intermediates prior to aromatization or the amino-acetonitrile is oxidized by the chlorine-sulfur dichloride mixture to cyanogen which is known to react with the sulfur chlorides to form 39 (see Section II,B,4). 

There are no systematic studies on the reaction of sulfur dichloride with polar organometallic reagents. The high reactivity of sulfur dichloride allows the couplings to be carried out at very low temperatures, even at —100 °C the reactions proceed almost instantaneously. The use of an excess of SC12 should be avoided, since this reactive molecule may easily add to the hetero-aromatic system or form an (unstable) sulfonium compound with the sulfur between the two heterocyclic units. 

Sulfurdiimides are obtained from aromatic amines and sulfur tetrafluoride. Heating of A-arylsulfonylimido dichlorides with aromatic amines affords A-aryl-A -sulfonylarylsulfurdiimides. The latter compounds are also formed in the stepwise replacement of the arylsulfonyl moiety in bis-arylsulfonylsulfurdiimides with aromatic amines. The [4+2] cycloaddition reactions of sulfurdiimides, which proceed in high yields, were extensively investigated. 

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