"Divergent Total Synthesis of (-)-Rhazinilam, (-)-Leucomidine B and (+)-Leuconodine F" and "Synthetic Studies Towards Sarpagine-Related Indoles"

The work presented in this thesis focuses on the synthesis of monoterpene indole alkaloids. The first part describes the divergent total synthesis of (-)-rhazinilam, (-)-leucomidine B and (+)-leuconodine F, three structurally distinct natural products of the Aspidosperma family. The key step involves the heteroannulation of an advanced tetrahydropyridine with bromoacetaldehyde or oxalyl chloride in order to afford the corresponding tetrahydroindolizine and 2,3-dioxopyrrole moieties, respectively. By fine tuning of the reaction conditions, the former was converted into rhazinilam while the latter led to the syntheses of leucomidine B and leuconodine F. In the case of leucomidine B, the development of a substrate-directed diastereoselective reduction of a sterically unbiased double bond is also discussed. The second part details the synthetic studies towards various members of the Sarpagan family. After the exploration of several strategies and indoles alkaloids, the enantioselective total synthesis of N(1)-demethyl-3,5-diepi-alstolactone was accomplished. This synthesis features three key points: 1) the incorporation of a vinyl ketone function in the C-2 position of indole by using the Liebeskind-Srogl coupling in order to afford, after ring-closing metathesis, an advanced eight-membered cyclic enone, 2) a highly diastereoselective intramolecular Michael addition and 3) the formation of an azabicyclo[3.3.1]nonane bridged system from the corresponding eight-membered ring via a dehydration / transannular cyclization process.