Expedient Construction of the ABEF Azatetracyclic Ring Systems of Lycoctonine-Type and 7,17-seco-Type C₁₉-Diterpenoid Alkaloids

Abstract

A synthetic strategy for the modeling construction of the highly bridged azatetracyclic ABEF ring system of numerous lycoctonine-type C19-diterpenoid alkaloids bearing a characteristic oxygenated quaternary center at C-7 has been successfully developed. The tetracyclic core was constructed rapidly from a readily prepared 6,7-bicyclic AB ring precursor through a 13-step sequence via an advanced tetracyclic N,O-acetal intermediate, which belong to another core structure of natural 7,17-seco-type alkaloids. The key step involves an SmI2-promoted intramolecular radical coupling reaction of an N,O-acetal with a carbonyl group, mimicking a plausible biogenetic transformation.

Diterpenoid Alkaloids from the Aerial Parts of Aconitum flavum Hand.-Mazz

“…Flavumoline Moreover, the benzoyl group was placed at C-14 according to the HMBC correlation from H-14 (δ H 5.07, s) to carbonyl (δ C 166.7, s). Three methoxy units were located at C-1, C- 16 Biogenetically, the configurations of H-5, 9, 10, could be ascribed to β-orientation whereas H-17 to α-orientation, which could be confirmed by ROESY correlations of H-5/9/10/12β and H-17/12α, respectively [21]. Then, the α-orientation of the benzoyl group at C-14 was determined on the ROESY correlations between H-14 and H-9.…”

“…Biogenetically, the configurations of H-5, 9, 10, could be ascribed to β- orientation whereas H-17 to α -orientation, which could be confirmed by ROESY correlations of H-5/9/10/12 β and H-17/12 α , respectively [ 21 ]. Then, the α -orientation of the benzoyl group at C-14 was determined on the ROESY correlations between H-14 and H-9.…”

The Palladium-Catalysed Intramolecular Alder-ene (IMAE) Reactions of Certain Heteroatom-Linked 1,6-Enynes: The Formation of Hexahydro-Indoles and -Benzofurans

“…[15] Extensions of such Ru-catalysed processes to the synthesis of certain alkaloid frameworks have been reported recently. [16] Reductive cycloisomerisations of 1,6-enynes catalysed by either palladium or rhodium have been reported by Trost and Rise [17] and Jang and Kirsche, [18] respectively. In the first case (involving palladium) either triethylsilane or polymethylhydrosiloxane (PMHS) serves as the reducing agent, while dihydrogen is employed for the same purpose in the second (i.e.…”

Die Invasion der Stechmücken

“…Hydroboration–oxidation22 of olefin 27 gave the primary alcohol 28 . DMP oxidation of 28 afforded a labile aldehyde, which was immediately subjected to an exclusive alkylation on treatment with potassium tert ‐butoxide and methyl iodide, delivering the methyl group to the β‐face to give 29 in 87 % yield 8d. Pleasingly, attempt to oxidize aldehyde to acid using Pinnick oxidation23 resulted in direct formation of lactone 30 in 90 % yield, completing the whole hexacyclic skeleton of spiramilactone B.…”