Rearrangements in the Furan Series. II. The Reaction Between Furfuraldehyde and Aromatic Amines

A survey of the reaction of a variety of primary aromatic amines with furfuraldehyde has shown that, in most cases, the product isolated has the 2,4-diarylaminocyclopent-2-enone structure as established in the case of aniline. In a number of cases the products were shown to be the isomeric 4,5-diarylamino derivatives. It has been established that the 2,4-diarylamino derivatives are the more stable structures and that 4,5-disubstituted isomers are intermediates. Treatment of the 4,5-diarylaminocyclopent-2-enones with mineral acids gives a facile ring opening at room temperature to form the corresponding Stenhouse salt. A mechanism is suggested for both the above reactions. The results of some previous work are clarified.