Trifluoroacetic anhydride ferrocene acylation

The relative sensitivity of furan to electrophilic attack stands in the order benzene < naphthalene < ferrocene < furan as found from competition experiments with styrene palladium(II) acetate.441 Relative rales for acylation by trifluoroacetic anhydride (no catalyst) arc observed to be thiophene (1), selenophene (6.5), furan (1.4 x 102), pyrrole (5.3 x I07), and... 

An efficient and ecofriendly procedure for the small-scale acylation of ferrocene with carboxylic acids is based on the in situ production of the mixed carboxylic-triflic anhydride (Table 4.15 see also Chapter 3). The reaction is simply performed by adsorbing ferrocene on the surface of activated alumina (preheated at 150°C for 3 h) and adding a mixture of carboxylic acid and trifluoroacetic anhydride (TFAA) at room temperature for a selected time. Products 40 are recovered in 55%-98% yield simply by elution with diethyl ether. 

Roberts and Wells354 were the first to use triflic acid in the acylation of phospha-ferrocenes with acetic anhydride and benzoic anhydride to afford ketophosphaferro-cenes in good yields (62-78%). Recently, acyl trifluoroacetates in excess triflic acid have been shown to be even more effective reagents355 [Eq. (5.141)]. 

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