Interrupted Fischer indolization approach toward the communesin alkaloids and perophoramidine

Synthesis of Functionalized Tetrahydroquinoline Containing Indole Scaffold via Chemoselective Annulation of Aza-ortho-quinone Methide Precursor

The chemoselective annulation of aza-ortho-quinone methide generated by in situ o-chloromethyl sulfonamide has been achieved with bifunctional acyclic olefin. This efficient approach provides access to the diastereoselective synthesis of functionalized tetrahydroquinoline derivatives containing indole scaffolds through the inverse-electron-demand aza-Diels-Alder reaction under mild reaction conditions with excellent results (up to 93% yield, > 20:1 dr). Moreover, this article realized the cyclization of α-halogeno hydrazone with electron-deficient alkene affording the tetrahydropyridazine derivatives, which had never been reported.

Ag(I)/PPh3-catalyzed diastereoselective syntheses of spiro[indole-3,4'-piperidine] derivatives via cycloisomerizations of tryptamine-ynamides

A Ag(I)/PPh₃-catalyzed chelation-controlled cycloisomerization of tryptamine-ynamide was developed to access the spiro[indole-3,4'-piperidine] scaffold in a racemic and diastereoselective manner. The diastereoselective products were achieved by a chiron approach. Density functional theory (DFT) calculations indicated that strong non-covalent effects between the substrate and catalyst/ligand complex stabilized the spiroindoleninium intermediate via cation-π-π interactions.

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.

Total Syntheses of Dihydroindole Aspidosperma Alkaloids: Reductive Interrupted Fischer Indolization Followed by Redox Diversification

We report a novel reductive interrupted Fischer indolization process for the concise assembly of the 20-oxoaspidospermidine framework. This rapid complexity generating route paves the way toward various dihydroindole Aspidosperma alkaloids with different C-5 side chain redox patterns. The end-game redox modulations were accomplished by modified Wolff-Kishner reaction and photo-Wolff rearrangement, enabling the total synthesis of (-)-aspidospermidine, (-)-limaspermidine, and (+)-17-demethoxy-N-acetylcylindrocarine and the formal total synthesis of (-)-1-acetylaspidoalbidine.

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

We report 8‐step syntheses of (−)‐minovincine and (−)‐aspidofractinine using easily available and inexpensive reagents and catalyst. A key element of the strategy was the utilization of a sequence of cascade reactions to rapidly construct the penta‐ and hexacyclic frameworks. These cascade transformations included organocatalytic Michael‐aldol condensation, a multistep anionic Michael‐S_N2 cascade reaction, and Mannich reaction interrupted Fischer indolization. To streamline the synthetic routes, we also investigated the deliberate use of steric effect to secure various chemo‐ and regioselective transformations.

Harnessing interrupted Fischer in continuous flow: sustainable synthesis of (spiro)indolenine and (spiro)indoline privileged scaffolds

3,3-Disubstituted indolenines are obtained via a green and sustainable flow chemistry protocol for interrupted Fischer indolisation reactions.

Total Synthesis as a Vehicle for Collaboration

"Collaboration" is not the first word most would associate with the field of total synthesis. In fact, the spirit of total synthesis is all-too-often reputed as being more competitive, rather than collaborative, sometimes even within individual laboratories. However, recent studies in total synthesis have inspired a number of collaborative efforts that strategically blend synthetic methodology, biocatalysis, biosynthesis, computational chemistry, and drug discovery with complex molecule synthesis. This Perspective highlights select recent advances in these areas, including collaborative syntheses of chlorolissoclimide, nigelladine A, artemisinin, ingenol, hippolachnin A, communesin A, and citrinalin B. The legendary Woodward-Eschenmoser collaboration that led to the total synthesis of vitamin B₁₂ is also discussed.

Pardon the Interruption: A Modification of Fischer's Venerable Reaction for the Synthesis of Heterocycles and Natural Products

This account provides an overview of our laboratory's studies of an unusual variant of the Fischer indolization reaction. We describe the discovery of the so-called 'interrupted Fischer indolization' and the development of the reaction from a methodological standpoint. In addition, our efforts to evaluate and apply this methodology in the context of akuammiline alkaloid total synthesis are discussed.

Recent Advances on the Total Syntheses of Communesin Alkaloids and Perophoramidine

The communesin alkaloids are a diverse family of Penicillium-derived alkaloids. Their caged-polycyclic structure and intriguing biological profiles have made these natural products attractive targets for total synthesis. Similarly, the ascidian-derived alkaloid, perophoramidine, is structurally related to the communesins and has also become a popular target for total synthesis. This review serves to summarize the many elegant approaches that have been developed to access the communesin alkaloids and perophoramidine. Likewise, strategies to access the communesin ring system are reviewed.

Stereochemical evaluation of bis(phosphine) copper catalysts for the asymmetric alkylation of 3-bromooxindoles with α-arylated malonate esters

An improved method for the asymetric alkylation of 3-bromooxindoles with α-arylated malonate esters is described. The asymmetric alkylation demonstrated was achieved up to 70% ee utilizing a copper(II) bis(phosphine) complex.

Catalytic asymmetric dearomatizing redox cross coupling of ketones with aryl hydrazines giving 1,4-diketones

An asymmetric Brønsted acid catalyzed dearomatizing redox cross coupling reaction has been realized, in which aryl hydrazines react with ketones to deliver 1,4-diketones, bearing an all-carbon quarternary stereocenter in high enantiopurity.

Evolution of a unified, stereodivergent approach to the synthesis of communesin F and perophoramidine

Expedient synthetic approaches to the highly functionalized polycyclic alkaloids communesin F and perophoramidine are described using a unified approach featuring a key decarboxylative allylic alkylation to access a crucial and highly congested 3,3-disubstituted oxindole. Described are two distinct, stereoselective alkylations that produce structures in divergent diastereomeric series possessing the critical vicinal all-carbon quaternary centers needed for each synthesis. Synthetic studies toward these challenging core structures have revealed a number of unanticipated modes of reactivity inherent to these complex alkaloid scaffolds. Additionally, several novel and interesting intermediates en route to the target natural products, such as an intriguing propellane hexacyclic oxindole encountered in the communesin F sequence, are disclosed. Indeed, such unanticipated structures may prove to be convenient strategic intermediates in future syntheses.

Cascade reactions: a driving force in akuammiline alkaloid total synthesis

The akuammiline alkaloids are a family of intricate natural products which have received considerable attention from scientists worldwide. Despite the fact that many members of this alkaloid class were discovered over 50 years ago, synthetic chemistry has been unable to address their architectures until recently. This minireview provides a brief overview of the rich history of the akuammiline alkaloids, including their isolation, structural features, biological activity, and proposed biosyntheses. Furthermore, several recently completed total syntheses are discussed in detail. These examples not only serve to highlight modern achievements in alkaloid total synthesis, but also demonstrate how the molecular scaffolds of the akuammilines have provided inspiration for the discovery and implementation of innovative cascade reactions for the rapid assembly of complex structures.

A diastereodivergent synthetic strategy for the syntheses of communesin F and perophoramidine

An efficient, unified, and stereodivergent approach toward communesin F and perophoramidine was examined. The C(3) all-carbon quaternary center of an oxindole was smoothly constructed by base-promoted indolone-malonate alkylation chemistry. The complementary relative stereochemistry of the crucial vicinal quaternary centers found in communesin F and perophoramidine was selectively installed by substrate-controlled decarboxylative allylic alkylations.

Studies toward communesin F: a Diels-Alder approach

A Diels-Alder reaction is used as a key step in a synthetic study toward communesin F, in order to simultaneously introduce both of the all-carbon quaternary stereocenters with complete control of relative stereochemistry. Further manipulations of the cycloadduct, toward the hexacyclic core-structure of communesin F, are also disclosed.

Interrupted Fischer-indole intermediates via oxyarylation of alkenyl boronic acids

The oxyarylation of alkenyl boronic acids with N-arylbenzhydroxamic acids has been achieved under both copper-mediated and copper-catalyzed conditions to provide access to interrupted Fischer-indole intermediates. This transformation is believed to proceed through a copper-promoted C-O bond forming event followed by a [3,3] rearrangement. The scope of the method is described and mechanistic experiments are discussed.