Diarylboryl hexachloroantimonate

Other derivatives of carboxylic acids and some unusual catalyst systems have found favor. Diarylboryl hexachloroantimonates activate acyl chlorides, carboxylic anhydrides and acyl enolates. A number of metal oxides have been successfully employed. It is worth noting at this point that the chloroacetylium and bromoacetylium ions, which can be prepared in either Freon 113 or sulfur dioxide, are more stable than the acetylium ion and have been shown to give high yields of ketones at low temperatures. ... 

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