Fluorenones Friedel-Crafts reaction

Concerning electrophilic side reactions, intramolecular Friedel-Crafts condensations have been reported for example, fluorenone is formed from 2-benzoylbenzenediazonium tetrafluorobo-rate.241 The strong Lewis acid boron trifluoride can also be responsible for side reactions, such as the extensive formation of tars from nitro-substituted arenediazonium tetrafluorobor-ates or the acidic hydrolysis of ester substituents, especially in the case of 2-(ethoxycar-bonyl)benzenediazonium tetrafluoroborate.105,242... 

Since the initial work of Chardonnens and others, few examples of syntheses of [l,2-a]IF derivatives exist outside of patent literature. Shi et al. recently reported [l,2-a]IFs 48a,b and [2,l-c]IFs 49a,b (Scheme 10) [46]. Diels-Alder reaction of alkynes 45a,b, readily available from fluorenones 44a,b, provided regioisomeric mixtures of diols 46a,b and 47a,b. Subsequent acid-catalyzed Friedel-Crafts condensation gives 48 and 49. The two derivatives of both regioisomers showed quantum yields in solution of 60% and showed good thermal stability, with decomposition occurring at temperatures greater than 330 °C. 

SCHEME 3.15 Fluorenone and related ketones synthesis via Friedel-Crafts acylation reaction with Nafion. 

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