Dicationic species superacid-promoted

Acyl-transfer reactions are some of the most important conversions in organic chemistry and biochemistry. Recent work has shown that adjacent cationic groups can also activate amides in acyl-transfer reactions. Friedel-Crafts acylations are known to proceed well with carboxylic acids, acid chlorides (and other halides), and acid anhydrides, but there are virtually no examples of acylations with simple amides.19 During studies related to unsaturated amides, we observed a cyclization reaction that is essentially an intramolecular acyl-transfer reaction involving an amide (eq 15). The indanone product is formed by a cyclization involving the dicationic species (40). To examine this further, the related amides 41 and 42 were studied in superacid promoted conversions (eqs 16-17). It was found that amide 42 leads to the indanone product while 41... 

Superacid-promoted dicationic species containing heteroaromatic rings, where positive charge centres migrate through consecutive deprotonation-reprotonation steps, undergo cyclization reactions followed by aromatization and superacid-promoted elimination of benzene (Scheme 10).31 The process leads to the synthesis of aza-polycyclic aromatic compounds in moderate to good yields. Seven examples include pirazole, oxazole, and thiazole heterocycles. 

Another novel class of oxonium dications involves the superacid-promoted ring opening reactions of oxazolines and related conversions.61 Oxazolines are well known for their ability to react with strong nucleophiles (i.e. alcohols) when protonated at the ring nitrogen 62 It was shown that the dicationic species (161 or 162) are capable of reacting with weak nucleophiles such as benzene (eq 52). 

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