Alkaloids of Tabernaemontana riedelii and T. rigida

Total Syntheses of (−)‐Minovincine and (−)‐Aspidofractinine through a Sequence of Cascade Reactions

“…[1,16] While several routes have been developed to construct racemic aspidofractinine, [23,24] its only asymmetric synthesis was reported by Gagnon and Spino [25] in 2009. The relative ease of our minovincine synthesis served as an impetus for developing a biosynthetically inspired synthesis of (À)-aspidofractinine (6). Specifically, we envisioned a Fischer indolization [26] interrupted by the pendant acetyl nucleophile.…”

“…Additionally, this unique aspidospermane derivative can be transformed to pauciflorine- [4] and eburnane-type [5] alkaloids (4, 5 in Figure 1) in few chemical steps. Owing to the apparent synthetic significance of minovincine (1), it has been an attractive research target since its isolation [6] in 1962. [7] Interestingly, and despite the advances of catalytic asymmetric methods, only two enantioselective approaches have been reported by MacMillan [8] and Nishida.…”

“…Our hope was also to expand our synthetic strategy toward topologically different minovincine-derived natural products. Therefore, a refractine-type alkaloid was also targeted, the hexacyclic (À)-aspidofractinine (6). As an overarching goal, we aimed to devise streamlined synthetic routes that would achieve high levels of "ideality" [10] and synthetic practicality.…”

A Review on Recent Developments in Syntheses of the Post-Secodine Indole Alkaloids. Part I: The Primary Alkaloid Types

“…The tendency of "naturally" configured tetracyclic aminoesters to undergo preferential lactam formation is further illustrated by Szántay et al 46 with their formal total synthesis of (±)-N-acetyl-12-demethoxycylindrocarine (96), whose (-)-enantiomer is contained in Tabernaemontana 48 primary amine 103a as an alternative to amine 69, which permitted isolation of the secodine-type intermediates, Scheme 17. Thus, condensation of rather unstable amine 103a, freshly prepared from the trityl derivative 103b, with aldehyde ester 6 afforded stable, crystalline lactam 104a in 79% yield.…”

Synthesis of Vinca Alkaloids and Related Compounds. 90.1 New Results in the Synthesis of Alkaloids with the Aspidospermane Skeleton. First Total Synthesis of (±)-3-Oxominovincine

“…This paper is an account of the successful continuation of the above research. (+)-3-Oxominovincine ( 14 ), isolated from Tabernaemontana riedelii , has only been prepared up to now by the oxidation of (+)-minovincine ( 17 ) . Several total syntheses of the latter alkaloid are known, and the corresponding papers mentioned that the β-acetyl group of the enamines used in those experiments (e.g., 3 , where R 1 = H; R 2 = COCH 3 ) did not split off even at high temperatures, i.e., in boiling toluene or xylene …”