Total Synthesis of Akuammiline Alkaloid (−)-Vincorine via Intramolecular Oxidative Coupling

Bioinspired Oxidative Cyclization of the Geissoschizine Skeleton for the Total Synthesis of (-)-17-nor-Excelsinidine

We report the first total synthesis of (-)-17-nor-excelsinidine, a zwitterionic monoterpene indole alkaloid that displays an unusual N4-C16 connection. Inspired by the postulated biosynthesis, we explored an oxidative coupling approach from the geissoschizine framework to forge the key ammonium-acetate connection. Two strategies allowed us to achieve this goal, namely an intramolecular nucleophilic substitution on a 16-chlorolactam with the N4 nitrogen atom or a direct I₂ -mediated N4-C16 oxidative coupling from the enolate of geissoschizine.

Alkaloid Synthesis Using Organocatalysts

This chapter covers the literature since the advent, in the 21st century, of total syntheses of alkaloids using enantio- or diastereoselective organocatalytic reactions to construct the alkaloid scaffolds. The details of these alkaloid syntheses are described separately for each basic skeleton, including indole, indoline, oxindole, and piperidine alkaloids.

Total synthesis of strictamine: a tutorial for novel and efficient synthesis

The novelty and efficiency of the overall synthetic route are the key values being imparted to the younger generation of synthetic chemists. In this Highlights, synthesis of strictamine was tutored to students on the creativity of synthetic design.

Oxidative coupling strategies for the synthesis of indole alkaloids

Direct functionalization of indole through oxidative coupling reactions with enolates or phenols provides a powerful tool for assembling indole alkaloids.

Diverting Reactive Intermediates Toward Unusual Chemistry: Unexpected Anthranil Products from Davis-Beirut Reaction

The discovery of a new variation on the Davis-Beirut reaction is described in which an atypical heterocyclic framework (the anthranil or benzo[c]isoxazole framework) is formed as the result of diversion of a key reactive intermediate away from its expected reactivity-a potentially general approach to reaction design and development. Experimental and computational support for the proposed mechanism and origins of altered reactivity are described.

Unified Total Syntheses of Structurally Diverse Akuammiline Alkaloids

The unified total syntheses of structurally diverse akuammiline alkaloids deformylcorymine (1), strictamine (2), and calophyline A (3) are reported. The strategy mimics the biosynthesis in nature at a strategic level, which allows for structural diversification from a common synthetic precursor by late-stage ring migrations.

Methods Utilizing First-Row Transition Metals in Natural Product Total Synthesis

First-row transition-metal-mediated reactions constitute an important and growing area of research due to the low cost, low toxicity, and exceptional synthetic versatility of these metals. Currently, there is considerable effort to replace existing precious-metal-catalyzed reactions with first-row analogs. More importantly, there are a plethora of unique transformations mediated by first-row metals, which have no classical second- or third-row counterpart. Herein, the application of first-row metal-mediated methods to the total synthesis of natural products is discussed. This Review is intended to highlight strategic uses of these metals to realize efficient syntheses and highlight the future potential of these reagents and catalysts in organic synthesis.

Recent advances on the total synthesis of alkaloids in mainland China

Alkaloids are a large family of natural products that mostly contain basic nitrogen atoms. Because of their intriguing structures and important functions, they have long been popular targets for synthetic organic chemists. China's chemists have made significant progress in the area of alkaloid synthesis over past decades. In this article, selected total syntheses of alkaloids from research groups in mainland China during the period 2011–16 are highlighted.

Recent progress in organocatalytic asymmetric total syntheses of complex indole alkaloids

Indole and its structural analogues have been frequently found in numerous alkaloids, pharmaceutical products and related materials. The enantioselective construction of these structures allows efficient total synthesis of optically pure indole alkaloids, and hence has received worldwide interest. In the past decade, asymmetric organocatalysis has been recognized as one of the most powerful strategies to create chiral molecules with high levels of stereoselectivity. In particular, organocatalytic asymmetric cascade reactions often occur with multiple bond-breaking and forming events simultaneously or sequentially, leading to the appearance of various straightforward approaches to access core structures for asymmetric total synthesis. This review will summarize recent applications of asymmetric organocatalysis in the enantioselective synthesis of indole alkaloids.

A 7-Step Formal Asymmetric Total Synthesis of Strictamine via an Asymmetric Propargylation and Metal-Mediated Cyclization

Herein is shown how a novel catalytic asymmetric propargylation of 3,4-dihydro-β-carboline, followed by a designed Au(I)/Ag(I)-mediated 6-endo-dig cyclization, can directly deliver the indolenine-fused methanoquinolizidine core of the akuammiline alkaloid strictamine in its native oxidation state, ultimately achieving a 7-step formal asymmetric total synthesis. Also demonstrated are how the cyclization products can rearrange into vincorine-type skeletons and a further use for the developed propargylation with the first catalytic asymmetric total synthesis of decarbomethoxydihydrogambirtannine.

Formal total synthesis of the akuammiline alkaloid (+)-strictamine

An asymmetric formal total synthesis of the akuammiline alkaloid (+)-strictamine is reported.

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.

Radicals: Reactive Intermediates with Translational Potential

This Perspective illustrates the defining characteristics of free radical chemistry, beginning with its rich and storied history. Studies from our laboratory are discussed along with recent developments emanating from others in this burgeoning area. The practicality and chemoselectivity of radical reactions enable rapid access to molecules of relevance to drug discovery, agrochemistry, material science, and other disciplines. Thus, these reactive intermediates possess inherent translational potential, as they can be widely used to expedite scientific endeavors for the betterment of humankind.

Total Synthesis of Calophyline A

Reported herein is the total synthesis of calophyline A, an indoline natural product possessing distinct ring connectivity which has not been synthesized previously. The synthetic route features several key transformations, including an aza-pinacol rearrangement to construct the nitrogen-containing bridged [3.2.2] bicycle, a Heck cyclization to assemble the fused 6/5/6/5 ring system, and a challenging late-stage aldol reaction to generate both a neopentyl quaternary stereogenic center and an oxygen-containing bridged [3.2.1] bicycle.

Asymmetric Total Syntheses of Aspidodasycarpine, Lonicerine, and the Proposed Structure of Lanciferine

Aspidodasycarpine and lonicerine are a pair of epimeric aspidophylline-type alkaloids bearing vicinal quaternary C7 and C16. The first and enantioselective total syntheses of these molecules are described here. A Ru-catalyzed asymmetric transfer hydrogenation established the first stereocenter. An Au-promoted Toste cyclization was exploited to assemble the bridged tetracyclic core and define the geometry of the exocyclic olefin; electron deficient (p-CF3C6H4)3P was a suitable ligand for this transformation. An aldol condensation followed by an intramolecular indole C3 alkylation constructed the adjacent quaternary C7 and C16 diastereoselectively, leading to a pentacyclic lactol as an advanced common intermediate for synthesizing both alkaloids. The proposed structure of lanciferine, a highly oxidized congener of aspidodasycarpine, was synthesized from the lactol by tuning the oxidation states of various carbons.

Catalytic Asymmetric Total Synthesis of (-)-Actinophyllic Acid

Described herein is a catalytic asymmetric total synthesis of (-)-actinophyllic acid, with the key step being a chiral phosphine-catalyzed [3 + 2] annulation between an imine and an allenoate to form a pyrroline intermediate in 99% yield and 94% ee. The synthesis also features CuI-catalyzed coupling between a ketoester and a 2-iodoindole to shape the tetrahydroazocine ring; intramolecular alkylative lactonization; SmI2-mediated intramolecular pinacol coupling between ketone and lactone subunits to assemble the complex skeleton of (-)-actinophyllic acid; and an unprecedented regioselective dehydroxylation.

Total Synthesis of (±)-Strictamine

The total synthesis of strictamine has been achieved in nine steps from a known enol triflate. Characteristic features of our approach included: a) creation of a C7 all-carbon quaternary stereocenter at an early synthetic stage; b) use of an N,N-dimethyl tertiary amine as a surrogate of the primary amine for the rapid build-up of a functionalized 2-azabicyclo[3,3,1]nonan-9-one skeleton (achieved by using a reaction sequence of α-bromination of the ketone, followed by a stereoconvergent intramolecular nucleophilic substitution reaction); and c) a late-stage construction of the indolenine unit.

Enantioselective Total Syntheses of Akuammiline Alkaloids (+)-Strictamine, (-)-2(S)-Cathafoline, and (-)-Aspidophylline A

The akuammiline alkaloids are a family of natural products that have been widely studied for decades. Although notable synthetic achievements have been made recently, akuammilines that possess a methanoquinolizidine core have evaded synthetic efforts. We report an asymmetric approach to these alkaloids, which has culminated in the first total syntheses of (-)-2(S)-cathafoline and the long-standing target (+)-strictamine. Moreover, the first enantioselective total synthesis of aspidophylline A is described.