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 15α-chloro-vincamine derivative 2 was prepared and proved to be key intermediate of a two-step transformation of apovincamine into vincamine. The structure of 2 was established via detailed NMR and X-ray investigations.