Total Syntheses of Aspidospermidine, N-Methylaspidospermidine, N-Acetylaspidospermidine, and Aspidospermine via a Tandem Cyclization of Tryptamine-Ynamide

Synthesis of Pyrrolidine-2-ylidenes from Isoxazolines and Allenes

A diastereoselective addition and rearrangement reaction has been developed for the synthesis of pyrrolidine-2-ylidenes from NH-isoxazolines and electron-deficient allenes. This method proceeds via the rearrangement of a proposed N-alkenylisoxazoline intermediate to generate densely functionalized pyrrolidine-2-ylidenes under simple catalyst-free conditions that tolerate ketone substituents and install relative stereochemistry at positions 3 and 4 of the heterocycle. Reaction optimization and the substrate scope are described in addition to studies evaluating the reactivity of the gem-dione and enaminone groups of the products.

Aza-Achmatowicz rearrangement coupled with intermolecular aza-Friedel-Crafts enables total syntheses of uleine and aspidosperma alkaloids

Aspidosperma and uleine alkaloids belong to the large family of monoterpene indole alkaloids with diverse biological activities and thus have attracted extensive synthetic interest. Reported is the development of a new synthetic strategy that allows direct C3-C2' linkage of indoles with functionalized 2-hydroxypiperidines to construct the core common to all aspidoserma and uleine alkaloids. Such indole-piperidine linkage is enabled by coupling aza-Achmatowicz rearrangement (AAR) with indoles via an intermolecular aza-Friedel-Crafts (iAFC) reaction. This AAR-iAFC reaction proceeds under mild acidic conditions with wide tolerance of functional groups (33 examples). The synthetic application of the AAR-iAFC method was demonstrated with collective total syntheses of 3 uleine-type and 6 aspidosperma alkaloids: (+)-3-epi-N-nor-dasycarpidone, (+)-3-epi-dasycarpidone, (+)-3-epi-uleine, 1,2-didehydropseudoaspidospermidine, 1,2-dehydroaspidospermidine, vincadifformine, winchinine B, aspidospermidine, and N-acetylaspidospermidine. We expect that this AAR-iAFC strategy is applicable to other monoterpene indole alkaloids with the C3-C2' linkage of indoles and piperidines.

Syntheses of Tetracyclic Indoline Derivatives Via Gold(I)-Catalyzed Hydroamination/Cycloisomerization Cascade of 2-Ethynyltryptamides

A gold(I)-catalyzed hydroamination/cycloisomerization cascade reaction was developed to yield indolizino[8,7-b]indole and indolo[2,3-a]-quinolizine derivatives from 2-ethynyltryptamides. The optimal conditions were determined by condition screening, and the functional group tolerances of these reactions were explored based on synthetic substrates. An insight into the explanation on the selectivity of the ring closure was obtained by density functional theory calculations. A plausible mechanism for the cascade reactions was proposed. Derivatization of the indolizino[8,7-b]indole and total synthesis of nauclefidine demonstrated the practicality of this strategy.

Methodological Development and Applications of Tryptamine-Ynamide Cyclizations in Synthesizing Core Skeletons of Indole Alkaloids

Over the past two decades, synthetic strategies for synthesizing the skeletons of various indole alkaloids based on tryptamine-ynamide have been continuously developed and applied to the total syntheses or formal total syntheses of related molecules. In this synopsis, we summarized the cyclization pathways of tryptamine-ynamide under different catalytic conditions, emphasizing the reaction mechanism and applications in the syntheses of indole alkaloids.

Aspidosperma and Strychnos alkaloids: Chemistry and biology

Of Nature's nearly 3000 unique monoterpene indole alkaloids derived from tryptophan, those members belonging to the Aspidosperma and Strychnos families continue to impact the fields of natural products (i.e., isolation, structure determination, biosynthesis) and organic chemistry (i.e., chemical synthesis, methodology development) among others. This review covers the biological activity (Section 2), biosynthesis (Section 3), and synthesis of both classical and novel Aspidosperma (Section 4), Strychnos (Section 5), and selected bis-indole (Section 6) alkaloids. Technological advancements in genetic sequencing and bioinformatics have deepened our understanding of how Nature assembles these intriguing molecules. The proliferation of innovative synthetic strategies and tactics for the synthesis of the alkaloids covered in this review, which include contributions from over fifty research groups from around the world, are a testament to the creative power and technical skills of synthetic organic chemists. To be sure, Nature-the Supreme molecular architect and source of a dazzling array of irresistible chemical logic puzzles-continues to inspire scientists across multiple disciplines and will certainly continue to do so for the foreseeable future.