Total Synthesis of 7‐ and 8‐Oxygenated Pyrano[3,2‐a]carbazole and Pyrano[2,3‐a]carbazole Alkaloids via Boronic Acid‐Catalyzed Annulation of the Pyran Ring

Abstract

The boronic acid-catalyzed annulation of citral opens up a short route to oxygenated cyclized monoterpenoid pyranocarbazole alkaloids. Thus, murrayamine-D is available in only three steps and 55% overall yield from the corresponding carbazole precursor.

Synthesis of Methylene‐Bridged Biscarbazole Alkaloids by using an Ullmann‐type Coupling: First Total Synthesis of Murrastifoline‐C and Murrafoline‐E

“…Biscarbazoles 6 and 7 would then become available by deprotection and pyran‐ring annulation by using either a C 5 or a C 10 building block. Various methods have been developed for this type of annulation, for example, the copper‐catalysed reaction with 2‐methyl‐3‐butyn‐2‐yl trifluoroacetate (the Godfrey procedure) or the treatment of a phenol with prenal and titanium(IV) isopropoxide or phenylboronic acid . The second route requires individual transformations of 9 a and 9 b to the protected derivatives 19 .…”

Nickel‐Catalyzed C(Aryl)−O Bond Activation/Cross‐Coupling Reaction of Carbazoles with Methyl Grignard: Synthesis of Ellipticine

“…When we performed the reactionwith different metal catalysts, such as palladium or cobalt, the reactiond id not proceed (Table 1, entries 12 and 13). Next, we investigated the effect of changing the solvent, but the desired productsw ere isolated in lower yields when the reactions were conducted in tetrahydrofuran( THF), 1,4-dioxane, and diethyle ther (Table 1, entries [14][15][16]. At room temperature, no product formation was observed (Table 1, entry 17).…”

Synthesis of Prenyl‐ and Geranyl‐Substituted Carbazole Alkaloids by DIBAL‐H Promoted Reductive Pyran Ring Opening of Dialkylpyrano[3,2‐a]carbazoles

“…2 A broad range of carbazoles belonging to these two classes has been isolated by the groups of Furukawa, Ito, Wu, and others from plants of the genera Murraya and Clausena (family: Rutaceae) 1. Diverse synthetic routes to pyrano[3,2‐ a ]carbazoles using different modes for annulation of the pyran ring have been described 3–5. On the other hand, many procedures have been developed for the selective introduction of prenyl groups by coupling reactions using transition metals 6–10.…”