The reaction of aromatic aldehydes 1 with 5,5-dimethyl-1,3-cyclohexanedione 2 was investigated by using [bmim][BF₄] as a reaction medium. It was found that without additional catalyst this reaction could only be realized at elevated temperature and gave a mixture of xanthenediones 3 and their ring-opening derivatives 2,2'-arylmethylenebis-(3-hydroxy-5,5-dimethyl-2-cyclohexen-1-one) (4) in poor yields. On the other hand, when it was carried out in the presence of FeCl₃•6H₂O, its selectivity and efficiency could be improved significantly and compound 3 could be obtained ex-clusively with high yield under optimized reaction conditions. Further study showed that when the same re-action was carried out under the catalysis of a combination of trimethylchlorosilane and FeCl₃•6H₂O, compound 4, without any contamination of 3, was obtained in good yield.

Key words: 6H₂O, ionic liquid, FeCl₃•, catalysis, xanthenedione