Approaches to the synthesis of alkaloids

As a preface to work leading to the total synthesis of 18,19-dehydrotabersonine, described in the following paper, some older work on the synthesis of (±)-3-oxo-20-desethyl-20-allylvincadifformine, its C-20 epimer, and (±)-3-oxo-19-vinylvincadifformine is reported. Attempts to convert these compounds,by appropriate manipulation of the isolated double bond, into a wide range of anilinoacrylate alkaloids, e.g. minovincine, tuboxenine, and pseudokopsinine, are described. Methods for the functionalisation of the double bond at an earlier stage in the synthesis, e.g. using 3,18-dioxo-1-demethylvincatine, have also been investigated.