F r i e s R e a r r a n g e m e n t i n F e r r o c e n e C h e m i s t r y Abstract: ortho-Ferrocenoylphenol (salicyloylferrocene) has been synthesized and treated with acetyl, propionyl, benzoyl and 2-furoyl chloride to obtain the corresponding (ortho-acyloxybenzoyl)ferrocenes, which were subjected to conditions for the Fries rearrangement. By treatment with AlCl 3 at room temperature in CH 2 Cl 2 they afforded the corresponding heteroanular derivatives, 1-acyl-1¢-(ortho-hydroxybenzoyl)ferrocenes in good to high yield. Under the same reaction conditions, but in the presence of ferrocene, all keto esters gave the corresponding monoacylferrocenes through an intermolecular Fries rearrangement.As a bifunctional ferrocene derivative, (ortho-hydroxybenzoyl)ferrocene [salicyloylferrocene, (1)] might be an interesting intermediate in the synthesis of other derivatives of this metallocene. To our knowledge, there are only two reports about its synthesis in the literature until present. Schaaf 1 synthesized this compound in about 20% overall yield by Friedel-Crafts acylation of ferrocene with o-methoxybenzoyl chloride (prepared in a separate experiment), followed by demethoxylation of the obtained (ortho-methoxybenzoyl)ferrocene. On the other hand, Nesmeyanov and coworkers 2,3 reported that this synthesis can be performed by a direct acylation of ferrocene with salicyloyl chloride (22%). Recently, we found 4 that ferrocene can be transformed into salicyloylferrocene in a one-step process, i.e. by acylation of this metallocene with a mixture of salicylic acid and phosphorus trichloride. Bearing in mind that the phenolic hydroxyl group can be protected/deprotected much more conveniently with an acetyl than with methyl group, we tried to acylate ferrocene with a mixture of acetyl salicylic acid and phosphorous trichloride. However, instead of the expected (ortho-acetoxy-benzoyl)ferrocene (2a) we obtained acetylferrocene (4a) formed in a transacylation process, i.e. an intermolecular Fries rearrangement took place. Because of this finding we decided to synthesize some (ortho-acyloxybenzoyl)ferrocenes in order to subject them the Fries rearrangement. 5,6 Here we report the results of these investigations.First of all, by reinvestigating reaction conditions described by us, 4 we found that the yield of (ortho-hydroxybenzoyl)ferrocene (1) can be improved to 40% by doubling the quantity of AlCl 3 and working with very diluted solutions. Compound 1 was then treated with acetic chloride or acetic anhydride in the presence of pyridine, affording (ortho-acetoxybenzoyl)ferrocene (2a) in almost quantitative yield (see Table 1 and Scheme 1). When ketoester 2a was treated with AlCl 3 in CH 2 Cl 2 at room temperature the reaction mixture became intensive dark violet, similar to the classical acylation of ferrocene by acyl chlorides in the presence of the same catalyst. This color was attributed to the formation of an intermediary complex between a more or less developed acylium cation and the corresponding aluminate, as depicted in the S...