Synthetic strategies to the ergoline ring system of ergot alkaloids

The synthetic strategies to the ergoline ring system (I) have been outlined, and discussed in terms of their yields and limitations. The total syntheses of ergoline, racemic and natural dihydrolysergic acid, lysergic acid, isosetoclavine, penniclavine, elymoclavine and chanoclavine-I have been described. These illustrate the synthetic problems that have been encountered in ergoline chemistry. The role of key intermediates has been emphasised. Modification to the original schemes have not given yields or procedures that can compete with the production by fermentation of ergot alkaloids. However, it is hoped that the synthetic strategies discussed in this article will provide useful information, when considering new approaches, or modification, to the unique heterocyclic ring system of ergoline.