Regioselective 6-Endo Cyclizations of 2-Indolylacyl Radicals:  Total Synthesis of the Pyrido[4,3-b]carbazole Alkaloid Guatambuine

Abstract

A regioselective 6-endo reductive cyclization of 2-indolylacyl radicals constitutes the key step of a straightforward synthetic entry to the olivacine skeleton, illustrated by a total synthesis of the tetrahydropyridine alkaloid guatambuine.

Concise Total Syntheses of Pyr­ido[4,3‐b]carbazole Alkaloids Using Copper‐Mediated 6π‐Electrocyclization

“…Removal of the N‐ Boc group in 33 was effected with BBr 3 in CH 2 Cl 2 at –78 °C to provide (±)‐guatambuine ( 9 ) in 60 % yield. The NMR spectroscopic data of 9 were in good agreement with previously reported data 19c. Additionally, the N‐ Boc group in 33 was cleaved by treatment with Cs 2 CO 3 in refluxing MeOH/THF to render 9a .…”

Synthesis and Anti-Tuberculosis Activity of Olivacine and Oxygenated Derivatives

“…In conclusion, we have developed a straightforward synthesis of olivacine (1) Supplementary Materials: Copies of the 1 H NMR, 13 C NMR and 2D NMR spectra.…”

“…Starting from commercial benzaldehyde 11, which can also be obtained almost quantitatively in one step from the much cheaper m-anisaldehyde [18], amide 12 is prepared by a three-step sequence of Henry reaction, LAH reduction and N-acetylation (Scheme 2) [19]. Bischler-Napieralski cyclization using phosphorus oxychloride led to the corresponding dihydroisoquinoline which was fully aromatized to 6-methoxy-1,5-dimethylisoquinoline (13) by dehydrogenation with palladium on charcoal in the presence of cyclohexene as additive. Cleavage of the methyl ether afforded the isoquinolinol which on reaction with trifluoromethanesulfonic anhydride provided the known isoquinolinyl triflate 14 [20] in 58% yield over seven steps.…”

“…Despite its side effects, elliptinium acetate (3) has reached the status of a licensed drug for the treatment of advanced breast cancer [9]. Diverse total syntheses of olivacine (1) have been reported [10][11][12][13][14][15]. Surprisingly, the pharmacological potential of olivacine (1) and its oxygenated derivatives (for example 4 and 5) has been much less investigated [16].…”

A novel and facile synthesis of 3-(2-benzofuroyl)- and 3,6-bis(2-benzofuroyl)carbazole derivatives

“…Therefore, a number of methodologies for the construction of heterocycle-containing carbazoles have been reported in recent years [15–19]. Most heterocycle-containing carbazoles reported in the literature comprise a common heterocyclic ring moiety fused with a carbazole ring, such as pyridocarbazoles [20–21], thienocarbazoles [22–23], pyranocarbazoles, pyrrolocarbazoles [24–25], indolocarbazoles [26–28], and synthetic analogues thereof. However, there are very few reports in which the heterocyclic moiety is substituted with a carbazole unit.…”