Studies of a Diazo Cyclopropanation Strategy for the Total Synthesis of (−)-Lundurine A

Asymmetric Carbene Transfer: Enhancing Chemical Diversity for Drug Discovery

The quest to explore chemical space is vital for identifying novel disease targets, impacting both the effectiveness and safety profile of therapeutic agents. The tangible chemical space, currently estimated at a conservative 108 synthesized compounds, pales in comparison to the theoretically conceivable diversity of 1060 molecules. To bridge this vast gap, organic chemists are spearheading innovative methodologies that promise to broaden this limited chemical diversity. A beacon of this progressive wave is Asymmetric Carbene Transfer (ACT), a burgeoning strategy that significantly boosts molecular diversity with efficient bond-formation and precise chiral control. This review focuses on the capabilities of ACT in creating pharmaceutically significant molecules, encompassing an array of natural products and bioactive compounds. Through the lens of ACT, we discern its substantial influence on drug discovery, paving the way for novel therapeutic avenues by expanding the boundaries of molecular diversity. This review will shed light on prospective methodological developments of ACT and articulate their conceivable contributions to the medicinal chemistry arena.

Access to Trifluoromethylketones from Alkyl Bromides and Trifluoroacetic Anhydride by Photocatalysis

Aliphatic trifluoromethyl ketones are a type of unique fluorine-containing subunit which play a significant role in altering the physical and biological properties of molecules. Catalytic methods to provide direct access to aliphatic trifluoromethyl ketones are highly desirable yet remain underdeveloped, partially owing to the high reactivity and instability of trifluoroacetyl radical. Herein, we report a photocatalytic synthesis of trifluoromethyl ketones from alkyl bromides with trifluoroacetic anhydride. The reaction features dual visible-light and halogen-atom-transfer catalysis, followed by an enabling radical-radical cross-coupling of an alkyl radical with a stabilized trifluoromethyl radical. The reaction provides straightforward access to aliphatic trifluoromethyl ketones from readily available and cost-effective alkyl halides and trifluoroacetic anhydride (TFAA).

Lewis acid mediated cyclization: synthesis of 2 spirocyclohexylindolines

Herein, we report the synthesis of 2-spirocyclohexylindolines based on a Lewis acid mediated cyclization. This diastereoselective procedure provides the target structures in a straightforward way via dual activation.

Engaging DBFO as a C1N1 “two-atom synthon” in [3 + 2] cycloaddition reaction: synthesis of the energetic material 5-azidotetrazolate 1N-oxide

Employing 1,1-dibromoformaloxime as a novel C1N1 “two-atom synthon” for the synthesis of tetrazole-based energetic materials via an intramolecular [3 + 2] annulation in aqueous solution.

Non-Diazo C-H Insertion Approach to Cyclobutanones through Oxidative Gold Catalysis

Cyclobutanones are synthetically versatile compounds that often require extensive effort to access. Herein, we report a facile synthesis of cyclobutanones based on the C(sp³ )-H insertion chemistry of oxidatively generated gold carbenes. Various cyclobutanones were obtained in synthetically useful yields from substrates with minimal structural prefunctionalization. This discovery reveals new synthetic utilities of gold-catalyzed oxidative transformations of alkynones.

Stereoselective Synthesis of Vinylcyclopropa[b]indolines via a Rh-Migration Strategy

A mild rhodium catalytic system has been developed to synthesize vinylcyclopropa[b]indolines through cyclopropanation of indoles with vinyl carbenoids generated from ring opening of cyclopropenes in situ. By employing a Rh-migration strategy, the products can be obtained with good to excellent E:Z ratios (≤99:1) and complete diastereoselectivity (≤99:1). This method is easy, has a low catalyst loading, and works for a broad range of functionalities.

Development of the Vinylogous Pictet-Spengler Cyclization and Total Synthesis of (±)-Lundurine A

A novel vinylogous Pictet-Spengler cyclization has been developed for the generation of indole-annulated medium-sized rings. The method enables the synthesis of tetrahydroazocinoindoles with a fully substituted carbon center, a prevalent structural motif in many biologically active alkaloids. The strategy has been applied to the total synthesis of (±)-lundurine A.

Collective Total Synthesis of (-)-Lundurines A-C

A collective asymmetric total synthesis of lundurines A-C using l-pyroglutamic acid derived from the chiral pool is described. The key steps include a tandem reductive amination/lactamization sequence to introduce the pyrrolidinone ring, a palladium-catalyzed intramolecular direct C-H vinylation of indole to construct the crucial polyhydroazocine ring, and a Lewis acid promoted formal [3 + 2] cycloaddition/N₂ extrusion process to install the polysubstituted cyclopropyl ring.

Total syntheses of pyrroloazocine indole alkaloids: challenges and reaction discovery

Total syntheses of pyrroloazocine indole alkaloids (lapidilectines, grandilodines, lundurines and tenuisines) are discussed in terms of existing retrosynthetic solutions and novel reaction discoveries.

Total Synthesis of Lundurine and Related Alkaloids: Synthetic Approaches and Strategies

This review focuses on the total synthesis of lundurines A-C. Their main structural feature is a unique cyclopropa[b]indole core that has been found only in these alkaloids. In addition to this characteristic structure, the biological activity makes them as attractive synthetic targets. However, almost two decades passed from their isolation and structural determination in 1995 to their first total synthesis. The first part of this review summarizes the synthetic approaches to the tri- and tetracyclic ring systems of lundurine as well as an inter- and intramolecular cyclopropanation strategy that gives the cyclopropa[b]indole core. The second part presents a detailed description of four total syntheses that were reported from 2014 to 2016. In addition, the asymmetric total synthesis of the related alkaloids grandilodine C and lapidilectine B is described.

Concise Total Synthesis of Lundurines A-C Enabled by Gold Catalysis and a Homodienyl Retro-Ene/Ene Isomerization

The total synthesis of lundurines A–C has been accomplished in racemic and enantiopure forms in 11–13 and 12–14 steps, respectively, without protection/deprotection of functional groups, by a novel tandem double condensation/Claisen rearrangement, a gold(I)-catalyzed alkyne hydroarylation, a cyclopropanation via formal [3 + 2] cycloaddition/nitrogen extrusion, and a remarkable olefin migration through a vinylcyclopropane retro-ene/ene reaction that streamlines the endgame.