New Synthetic Routes to (+)-Uleine and (-)-Tubifolidine: General Approach to 2-Azabicyclo[3.3.1]nonane Indole Alkaloids

Asymmetric Divergent Total Syntheses of (+)-Decursivine and (+)- Serotobenine via Intramolecular Fischer Indole Synthesis

A new asymmetric synthetic route to (+)-decursivine and (+)-serotobenine is formulated. The key developments are the de novo construction of the crucial eight-membered 3,4-fused tricyclic indole ring engaged by the intramolecular Fischer indole synthesis and the stereocontrolled assembly of the dihydrobenzofuran subunit mediated by the asymmetric intramolecular Rh-carbenoid C-H insertion. BF₃-mediated selective C15 epimerization followed by removal of the amine masking groups completed the target natural compounds' asymmetric and divergent total syntheses.

Asymmetric Total Syntheses of Strychnos Alkaloids via Selective Fischer Indolization

The complex structures and important biological functions of Strychnos alkaloids have attracted a great deal of attention from synthetic chemists. Herein, we describe the concise asymmetric total syntheses of the Strychnos alkaloids, (-)-dehydrotubifoline, (-)-tubifoline, and (-)-tubifolidine, as well as the formal total synthesis of (-)-strychnine. Our strategy features the construction of the common tetracyclic pyrrolo[2,3-d]carbazole structure using regioselective Fischer indolization on unsymmetrical cyclic ketones and late-stage functionalization for divergent synthesis. We developed a stepwise Fischer indolization featuring selective formation of enol triflate to solve the challenging regioselectivity problem, leading to the common tetracyclic ring skeleton in these Strychnos alkaloids. The regioselectivity of Fischer indolization on unsymmetrical cyclic ketones was studied on the basis of different types of ring systems and supported by density functional theory calculations. Overall, our success in the construction of this tetracyclic ring secured the syntheses of Strychnos alkaloids and may provide a general method for the total syntheses of various alkaloids containing this skeleton.

Synthesis of indole derivatives as prevalent moieties present in selected alkaloids

Indoles are a significant heterocyclic system in natural products and drugs. They are important types of molecules and natural products and play a main role in cell biology. The application of indole derivatives as biologically active compounds for the treatment of cancer cells, microbes, and different types of disorders in the human body has attracted increasing attention in recent years. Indoles, both natural and synthetic, show various biologically vital properties. Owing to the importance of this significant ring system, the investigation of novel methods of synthesis have attracted the attention of the chemical community. In this review, we aim to highlight the construction of indoles as a moiety in selected alkaloids.