Criocerine analogues of type 3, when dissolved in acetic acid, form the novel dimeric compounds of type 6 whose structures were thoroughly investigated by NMR spectroscopic methods.
The dimerization products of criocerine (1) are different (2 or 3) depending on whether the reaction is carried out in acetic acid or trifluoroacetic acid. The highly strained product 3 rearranges spontaneously through a retro Diels-Alder reaction. All structures involved were thoroughly investigated by NMR spectroscopic methods.