Fluorene-9-carboxylic acid chloride

The first account of the indeno[2,l-a]fluorene core in the literature dates to 1939 when Weizmann investigated polycyclic structures and their potential carcinogenic properties [23]. Intramolecular Friedel-Crafts acylation of 3,6-diphenylphthalic anhydride (113) in refluxing CS2 afforded fluorenone carboxylic acid 114 (Scheme 33). Acid chloride formation and subsequent cyclization in concentrated sulfuric acid generated the parent indeno[2,l-a]fluorene dione 115 in 5% yield with respect to 113. This was reaffirmed by Deuschel in 1951 where 115 is obtained in 72% under the same conditions [26]. 

Cremlyn et aV examined the reaction of fluorene 39 with excess chlorosulfonic acid (six or twelve equivalents) or less reagent (three equivalents) in thionyl chloride. In each case, the product appeared to be a 1 1 mixture of the 2-sulfonyl chloride and the 2,7-disulfonyl chloride. The latter compoimd was obtained as the major product when fluorene-9-carboxylic acid was treated with a large excess of chlorosulfonic acid (twelve equivalents) in boiling chloroform (2 hours). ... 

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. ... 

Cyclodehydration Aluminum chloride see also Methyl fluorene-9-carboxylate). Dowtherm. Fluorosulfonic acid. Hydrogen fluoride. Perchloric add. Phosphorus pentoxide. Phosphoryl chloride. Polyphosphate ester. Polyphosphoric add. Potassium bisulfate. Sodium aluminum chloride. Sulfur trioxide-Dimelhylformamide. />-Toluenesulfonic acid. Trifluoroacetic acid. Trifluoroacetic anhydride. 

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