Total Syntheses of Anominine and Tubingensin A

Abstract

A divergent strategy for the total syntheses of the indole terpenoid anominine (1) and its natural congener tubingensin A (2) has been developed. The common intermediate 11 bearing all of the required stereogenic centers for both natural products was first assembled by employing a Ueno-Stork radical cyclization and a Sc(OTf)(3)-mediated Mukaiyama aldol reaction to form the key C-C bonds in a stereocontrolled manner. The route to anominine features a radical deoxygenation followed by an efficient side-chain installation, while the path to tubingensin A exploits a CuOTf-promoted 6π-electrocyclization/aromatization sequence to forge the central region of the pentacyclic scaffold.

Simple indole alkaloids and those with a nonrearranged monoterpenoid unit

“…Compound 279 was transformed to 277 in 9 steps, and 278 was obtained from 279 through Cu-mediated 6p-electrocyclization (Scheme 67). 108 A new monoterpenoid alkaloid alstilobanine A (280), isolated from the leaves of the Malayan plant Alstonia angustiloba, was synthesized. The key b-lactone intermediate 283 was derived from indole 2-acetic acid ester 281 through an the intermolecular addition of the enolate of 281 to nitrosoalkene 282 and an intramolecular Romo cyclization (a formal ketene/ketone [2 + 2] intramolecular cycloaddition) reaction.…”

Total synthesis and antiviral activity of indolosesquiterpenoids from the xiamycin and oridamycin families

“…A 6π-electrocyclization23 (path a) and a Heck-type annulation242526272829 (path b) were envisioned as two alternatives to forge the carbazole motif. The former draws on our recent syntheses of tubingensin A and daphenylline3031, while the latter relies on activation of the indole C2–H bond by palladium. Correspondingly, triene ( 7 ) and indosespene ester ( 8 ) are considered as the key intermediates for the two strategies.…”

“…Under the optimized conditions [Cp 2 TiCl 2 (20 mol%), Mn, i Pr 2 NEt, TMSCl], the desired trans -decalin 13 was obtained as a single diastereomer. TBS protection followed by acetyl deprotection gave 14 (44% yield for the three steps), which was subjected to a sequence of DMP oxidation, Grignard addition (with reagent 15 )30, and dehydration (MsCl/ i Pr 2 NEt) to furnish triene 16 in 75% overall yield. On microwave irradiation (120 °C, air), 16 underwent a thermal 6π-electrocyclization and a subsequent aromatization to generate carbazole 17 (80% yield).…”

Enantioselective Total Syntheses of Akuammiline Alkaloids (+)-Strictamine, (−)-2(S)-Cathafoline, and (−)-Aspidophylline A

“…Toward this endeavor, enal 20 was first oxidized by NIS in the presence of potassium carbonate in methanol 22 to provide enoate 21 . Next, treatment of enoate 21 with vinyl ether 22 and NIS furnished an intermediate mixed acetal bearing an iodide, 23 thus setting the stage for a Ueno–Stork cyclization. 24 Exposure of this compound to radical cyclization conditions efficiently delivered C7-alkylated product 23 with diastereocontrol about the two newly formed stereocenters.…”