Benzil with chlorosulfonic acid

Treatment of benzils with chlorosulfonic acid yields 2-arylbenzofurans (Scheme 67) <87JHC117>. 

Benzil 258 undergoes a novel cyclization reaction on treatinent with chlorosulfonic acid (six equivalents) at 40 °C (2 hours) to 5ueld 3-chloro-2-phenylbenzofuran-6,4 -disulfonyl chloride (259, 60%). The mechanism originally proposed for the reaction involved cyclization to the benzofuran ring system prior to sulfonation. However, this mechanism is probably incorrect and has been modified so that sulfonation occurs before cyclization as shown in Scheme 4,... 

Benzilic acid 294 was claimed to react with chlorosulfonic acid (12 equivalents) in boiling chloroform to give 4,4 -dichlorosulfonylbenzophenone 292, however repetition of the reaction afforded 9-chlorofluorene-2,7-disulfonyl chloride 295 (38%). The proposed mechanism for this conversion is shown in Scheme 8 and involves protonation of the alcoholic hydroxyl group followed by loss of water. The carbocation 296 is formed before cyclization to fluorene-9-carboxylic acid, so that subsequent sulfonation should occur in the 2,7-positions. ... 

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