Enantioselective Synthesis of Isocarbostyril Alkaloids and Analogs Using Catalytic Dearomative Functionalization of Benzene

Total synthesis of 1,4a-di-epi-ent-pancratistatin, exemplifying a stereodivergent approach to pancratistatin isomers

The total synthesis of 1,4a-di-epi-ent-pancratistatin, a novel stereoisomer of the anti-tumor Amaryllidaceae alkaloid pancratistatin, was achieved in 14 steps starting from D-mannitol. The construction of the pancratistatin skeleton involved conjugate addition of organocuprate to a nitrosoolefin, which was generated in situ from inosose oxime. This was followed by stereoselective reduction of the oxime to an amine and site-selective formylation. Biological evaluations revealed that the newly synthesized compounds exhibit cytotoxicity toward cancer cells and significant ferroptosis inhibitory activity. These compounds constitute a promising small-molecule library for the development of potent bioactive agents.

Immunosuppressive alkaloids from Narcissus tazetta subsp. Chinensis and the mechanism of (+)-narciclasine in vitro and in vivo

Three previously undescribed and sixteen known alkaloids were bioguidedly isolated from the bulbs of Narcissus tazetta subsp. chinensis (M.Roem.) Masamura & Yanagih. The structures were elucidated by spectroscopic data, including HRESIMS, NMR, and ECD. Eleven of the isolated alkaloids exhibited immunosuppressive activity on the proliferation of human T cells. (+)-Narciclasine (18) showed the most significantly suppressive activity with an IC50 value of 14 ± 5 nM. In vitro, (+)-narciclasine (18) blocked NF-κB signal transduction, but did not affect PI3K/AKT signal transduction. What was more, (+)-narciclasine significantly reduced ALT and AST levels and alleviated liver damage induced by ConA in AIH mouse model.

Recent Advances in Dearomative Partial Reduction of Benzenoid Arenes

Dearomative partial reduction is an extraordinary approach for transforming benzenoid arenes and has been well-known for many decades, as exemplified by the dehydrogenation of Birch reduction and the hydroarylation of Crich addition. Despite its remarkable importance in synthesis, this field has experienced slow progress over the last half-century. However, a revival has been observed with the recent introduction of electrochemical and photochemical methods. In this Minireview, we summarize the recent advancements in dearomative partial reduction of benzenoid arenes, including dihydrogenation, hydroalkylation, arylation, alkenylation, amination, borylation and others. Further, the intriguing utilization of dearomative partial reduction in the synthesis of natural products is also emphasized. It is anticipated that this Minireview will stimulate further progress in arene dearomative transformations.

Discovery and bioinspired total syntheses of unprecedented sesquiterpenoid dimers unveiled bifurcating [4 + 2] cycloaddition and target differentiation of enantiomers

[4 + 2] cycloaddition has led to diverse polycyclic chiral architectures, serving as novel sources for organic synthesis and biological exploration. Here, an unprecedented class of cadinane sesquiterpene [4 + 2] dimers, henryinins A-E (1-5), with a unique 6/6/6/6/6-fused pentacyclic system, were isolated from Schisandra henryi. The divergent total syntheses of compounds 1-5 and their enantiomers (6-10) were concisely accomplished in eight linear steps using a protection-free approach. Mechanistic studies illustrated the origin of selectivity in the key [4 + 2] cycloaddition as well as the inhibition of reaction pathway bifurcation via desymmetrization. The chemical proteomics results showed that a pair of enantiomers shared common targets (PRDX5 C100 and BLMH C73) and had unique targets (USP45 C588 for 4 and COG7 C419 for 9). This work provides experimental evidence for the discovery of unprecedented cadinane dimers from selective Diels-Alder reaction and a powerful strategy to explore the biological properties of natural products.

Rejuvenation of dearomative cycloaddition reactions via visible light energy transfer catalysis

Dearomative cycloaddition is a powerful technique to access sp3-rich three-dimensional structural motifs from simple flat, aromatic feedstock. The building-up of unprecedentedly diverse polycyclic scaffolds with increased saturation and stereochemical information having various applications ranging from pharmaceutical to material sciences, is an essential goal in organic chemistry. However, the requirement of large energy inputs to disrupt the aromaticity of an arene moiety necessitates harsh reaction conditions for ground state dearomative cycloaddition. The photochemical requirement encompasses use of ultraviolet (UV) light to enable the reaction on an excited potential energy surface. The microscopic reversibility under thermal conditions and the use of high energy harmful UV irradiation in photochemical manoeuvres, however, constrain their widespread use from a synthetic point of view. In this context, the recent renaissance of visible light energy transfer (EnT) catalysis has become a powerful tool to initiate dearomative cycloaddition as a greener and more sustainable approach. The excited triplet state population is achieved by triplet energy transfer from the appropriate photosensitizer to the substrate. While employing mild visible light energy as fuel, the process leverages an enormous potential of excited state reactivity. The discovery of an impressive portfolio of organic and inorganic photosensitizers with a range of triplet energies facilitates visible light photosensitized dearomative cycloaddition of various substrates to form sp3-rich fused polycyclic architectures with diverse applications. The tutorial review comprehensively surveys the reawakening of dearomative cycloadditions via visible light-mediated energy transfer catalysis in the past five years. The progress ranges from intra- and intermolecular [2π + 2π] to [4π + 2π], and ends at intermolecular [2π + 2σ] cycloadditions. Furthermore, the review provides potential possibilities for future growth in the growing field of visible light energy transfer catalysis.

Site selective gold(i)-catalysed benzylic C-H amination via an intermolecular hydride transfer to triazolinediones

Triazolinediones are known as highly reactive dienophiles that can also act as electrophilic amination reagents towards enolisable C-H bonds (ionic pathway) or weak C-H bonds (free radical pathway). Here, we report that this C-H amination reactivity can be significantly extended and enhanced via gold(i)-catalysis. Under mild conditions, several alkyl-substituted aryls successfully undergo benzylic C-H aminations at room temperature. The remarkable site selectivity that is observed points towards strong electronic activation and deactivation effects, that go beyond a simple weakening of the C-H bond. The observed catalytic C-H aminations do not follow the expected trends for a free radical-type C-H amination and show complementarity to existing methods. Density functional theory (DFT) calculations and distinct experimental trends provide a clear mechanistic rationale for observed selectivity patterns, postulating a novel pathway for triazolinedione-induced aminations via a carbon-to-nitrogen hydride transfer.

Electrochemical Preparation of Sm(II) Reagent Facilitated by Weakly Coordinating Anions

Samarium diiodide (SmI2 ) is widely used as a strong one-electron reducing agent and is often employed to form C-C bonds in complex systems. Despite their utility, SmI2 and related salts suffer from several drawbacks that render the use of Sm reducing agents in large-scale synthesis impractical. Here, we report factors influencing the electrochemical reduction of Sm(III) to Sm(II), towards the goal of electrocatalytic Sm(III) reduction. We probe the effect of supporting electrolyte, electrode material, and Sm precursor on Sm(II)/(III) redox and on the reducing power of the Sm species. We find that the coordination strength of the counteranion of the Sm salt affects the reversibility and redox potential of the Sm(II)/(III) couple and establish that the counteranion primarily determines the reducibility of Sm(III). Electrochemically generated SmI2 performs similarly to commercial SmI2 solutions in a proof-of-concept reaction. The results will provide fundamental insight to facilitate the development of Sm-electrocatalytic reactions.

Formation of Isolable Dearomatized [4 + 2] Cycloadducts from Benzenes, Naphthalenes, and N-Heterocycles Using 1,2-Dihydro-1,2,4,5-tetrazine-3,6-diones as Arenophiles under Visible Light Irradiation

We report that the dearomative [4 + 2] cycloaddition between 1,2-dihydro-1,2,4,5-tetrazine-3,6-diones (TETRADs) and benzenes, naphthalenes, or N-heteroaromatic compounds under visible light irradiation affords the corresponding isolable cycloadducts. Several synthetic transformations including transition-metal-catalyzed allylic substitution reactions using the isolated cycloadducts at room temperature or above were demonstrated. Computational studies revealed that the retro-cycloaddition of the benzene-TETRAD adduct proceeds via an asynchronous concerted mechanism, while that of the benzene-MTAD adduct (MTAD = 4-methyl-1,2,4-triazoline-3,5-dione) proceeds via a synchronous mechanism.

Total Synthesis of (+)-Pancratistatin and Its Potent Topo I Inhibition Activity Studies

As a preeminent anticancer natural product, (+)-pancratistatin has always been a privileged synthetic target. Herein, the total synthesis of (+)-pancratistatin is reported in 10 linear steps by utilizing a known aldehyde as chiral source. This synthetic route features a highly stereoselective intermolecular Michael addition and intramolecular Henry reaction to construct a cyclohexane ring bearing 6 successive stereocenters. Moreover, all of the synthetic steps are reliable and efficient and can be easily scaled up, which facilitated anticancer pharmacological tests of (+)-pancratistatin. Importantly, a new pharmacological mechanism of action was discovered for the first time where (+)-pancratistatin is able to inhibit the activity of topoisomerase I, which would pave the way for the development of new-type Topo I inhibitors.

Dearomative logic in natural product total synthesis

Covering: 2011 to 2022The natural world is a prolific source of some of the most interesting, rare, and complex molecules known, harnessing sophisticated biosynthetic machinery evolved over billions of years for their production. Many of these natural products represent high-value targets of total synthesis, either for their desirable biological activities or for their beautiful structures outright; yet, the high sp³-character often present in nature's molecules imparts significant topological complexity that pushes the limits of contemporary synthetic technology. Dearomatization is a foundational strategy for generating such intricacy from simple materials that has undergone considerable maturation in recent years. This review highlights the recent achievements in the field of dearomative methodology, with a focus on natural product total synthesis and retrosynthetic analysis. Disconnection guidelines and a three-phase dearomative logic are described, and a spotlight is given to nature's use of dearomatization in the biosynthesis of various classes of natural products. Synthetic studies from 2011 to 2021 are reviewed, and 425 references are cited.

Stereodivergent dehydrative allylation of β-keto esters using a Ru/Pd synergistic catalyst

α-Alkylation of a β-keto ester is a frequently used reaction for carbon–carbon bond formation. However, extension to a stereoselective reaction remains a significant challenge, because the product easily racemizes under acidic or basic conditions. Here, we report a hybrid system consisting of Pd and Ru complexes that catalyzes the asymmetric dehydrative condensation between cinnamyl-type allylic alcohols and β-keto esters. α-Non-substituted β-keto ester can be allylated to afford an α-mono-substituted product with high regio-, diastereo-, and enantioselectivity. No epimerization occurs owing to the nearly neutral conditions, which is achieved by a rapid proton transfer from Pd-enolate formation to Ru π-allyl complex formation. Four diastereomers can be synthesized on demand by changing the stereochemistry of the Pd or Ru complex. Eight stereoisomers with three adjacent stereogenic centers can be synthesized by employing diastereoselective reduction of the ketone in the products. The formal synthesis of (+)-pancratistatin demonstrates the utility of the reaction.

α-Alkylation of β-keto esters is a frequently used reaction for carbon–carbon bond formation, but a general, stereoselective version of this reaction is challenging to realize. Here, the authors report a combined ruthenium and palladium catalytic system for the asymmetric dehydrative condensation between cinnamyl-type allylic alcohols and β-keto esters.

HFIP in Organic Synthesis

1,1,1,3,3,3-Hexafluoroisopropanol (HFIP) is a polar, strongly hydrogen bond-donating solvent that has found numerous uses in organic synthesis due to its ability to stabilize ionic species, transfer protons, and engage in a range of other intermolecular interactions. The use of this solvent has exponentially increased in the past decade and has become a solvent of choice in some areas, such as C-H functionalization chemistry. In this review, following a brief history of HFIP in organic synthesis and an overview of its physical properties, literature examples of organic reactions using HFIP as a solvent or an additive are presented, emphasizing the effect of solvent of each reaction.

Discovery of glycosylated naphthacemycins and elucidation of the glycosylation

Two glycosylated naphthacemycins (naphthacemycins D₁ and D₂) were identified in Streptomyces sp. N12W1565. These two compounds not only showed antimicrobial potential against bacteria but also exhibited more aqueous solubility than naphthacemycins. Furthermore, the whole genome of Streptomyces sp. N12W1565 has been sequenced, the natY gene, located outside the biosynthetic gene cluster encoding a D-glucose glycosyltransferase, was identified to mediate glycosylation in the phenolic hydroxyl of the naphthacemycin core scaffold. Glycosyltransferase was elucidated in vitro by using a homologous enzyme, which showed potential as a biocatalyst.

Dearomatization [4+2] Cycloaddition of Nonactivated Benzene Derivatives

Dearomatization reactions have recently emerged as a powerful tool for the rapid buildup of molecular complexity. Here, an unparalleled thermal dearomatization [4+2] cycloaddition reaction between benzene derivatives and a 2H-phosphindole tungsten complex was reported. The unique reactivity of the in situ-generated 2H-phosphindole complex toward benzene was revealed by density functional theory calculations. We thus provide new insights into the dearomatization of nonactivated arenes and pave the way for the manipulation of the dearomatization for further applications.

Catalytic, Asymmetric Total Synthesis of (+)-α-, (+)-β-, (+)-γ-, and (-)-δ-Lycorane

The first collectively asymmetric total synthesis of all members of lycorane, including (+)-α, (+)-β, (+)-γ, and (-)-δ, in a catalytic manner has been achieved. The cornerstone of this synthesis features an asymmetric, stereodivergent Ir/amine dual catalytic α-allylation of 2-phthalimidoacetaldehyde.

N-Heterocyclic carbene (NHC)-catalyzed oxidation of unactivated aldimines to amides via imine umpolung under aerobic conditions

Herein, we disclose an NHC-catalyzed aerobic oxidation of unactivated aldimines for the synthesis of amides via umpolung of imines proceeding through an aza-Breslow intermediate. We have developed an eco-friendly method for the conversion of imines to amides by using molecular oxygen in air as the sole oxidant and dimethyl carbonate (DMC) as a green solvent under mild reaction conditions. Broad substrate scope, high yields and gram scale syntheses expand the practicality of the developed method.

A general NHC-catalyzed conversion of imines to amides proceeding through umpolung–oxidation under aerobic conditions in green solvent is reported.

An Oxidative Dearomatization Approach to Tetrodotoxin via a Masked ortho-Benzoquinone

Progress toward a stereoselective synthesis of tetrodotoxin (TTX) is presented. Oxidative dearomatization of a tetrasubstituted guaiacol arene yielded a masked ortho-benzoquinone that intercepted an acyl nitroso species generated in situ by the copper-catalyzed aerobic oxidation of an acyl hydroxylamine. The subsequent alkene dihydroxylation and reduction of a bis-neopentylic ketone proceeded with perfect diastereoselectivity to reveal advanced intermediates toward the synthesis of TTX.

Short, enantioselective, gram-scale synthesis of (-)-zephyranthine

A reasonable synthesis design by strategically integrating functional group manipulation into the ring system construction resulted in a short, enantioselective, gram-scale total synthesis of (−)-zephyranthine. The concise route includes a catalytic Michael/Michael cascade for the asymmetric synthesis of a penta-substituted cyclohexane with three contiguous stereogenic centers, a remarkable 8-step one-pot operation to easily assemble the zephyranthine tetracyclic skeleton, the regioselective construction of a double bond in the C ring and an asymmetric dihydroxylation. This synthesis is also flexible and paves a potential path to a variety of cyclohexylamine-fused tricyclic or polycyclic alkaloids.

A reasonable synthesis design by strategically integrating functional group manipulation into the ring system construction resulted in a short, enantioselective, gram-scale total synthesis of (−)-zephyranthine.

Recent Visible Light and Metal Free Strategies in [2+2] and [4+2] Photocycloadditions

When aiming to synthesize molecules with elevated molecular complexity starting from relatively simple starting materials, photochemical transformations represent an open avenue to circumvent analogous multistep procedures. Specifically, light-mediated cycloadditions remain as powerful tools to generate new bonds begotten from non-very intuitive disconnections, that alternative thermal protocols would not offer. In response to the current trend in both industrial and academic research pointing towards green and sustainable processes, several strategies that meet these requirements are currently available in the literature. This Minireview summarizes [2+2] and [4+2] photocycloadditions that do not require the use of metal photocatalysts by means of alternative strategies. It is segmented according to the cycloaddition type in order to give the reader a friendly approach and we primarily focus on the most recent developments in the field carried out using visible light, a general overview of the mechanism in each case is offered as well.

Theoretical Analysis of the Heterocyclic [4+2] Cycloaddition Between Pyridinium Ion and Enol Ether

Dearomative heterocyclic [4+2] cycloaddition between the N-(2,4-dinitrophenyl)pyridinium ion of nicotinamide and an enol ether was analyzed by Density Functional Theory (DFT) calculations. The calculation revealed that the reaction undergoes stepwise bond formation rather than occurring in a concerted manner. The experimental products were found to be both kinetically and thermodynamically favored. The calculated transition states and intermediate suggested that the high diastereoselectivity is derived from the electrostatic interaction between the 2-nitro group of the pyridinium ion and the hydrogen of the enol ether.

Electrophilic Aminating Agents in Total Synthesis

Classical amination methods involve the reaction of a nitrogen nucleophile with an electrophilic carbon center; however, in recent years, umpoled strategies have gained traction where the nitrogen source acts as an electrophile. A wide range of electrophilic aminating agents are now available, and these underpin a range of powerful C−N bond‐forming processes. In this Review, we highlight the strategic use of electrophilic aminating agents in total synthesis.

Total synthesis of natural products using photocycloaddition reactions of arenes

The photocycloaddition reaction of benzene with alkenes has become a significant approach for organic chemists and thus has been frequently utilized as a key step in the total synthesis of natural products. In this mini-review, the recent developments in [4 + 2] and [2 + 2] photocycloaddition reactions will be emphasized in constructing core scaffolds of complex natural products. By combining them together, we aim to demonstrate the utility and reinstate the importance of this methodology.

Advances in Catalytic Asymmetric Dearomatization

Asymmetric catalysis has been recognized as the most enabling strategy for accessing chiral molecules in enantioenriched forms. Catalytic asymmetric dearomatization is an emerging and dynamic research subject in asymmetric catalysis, which has received considerable attention in recent years. The direct transformations from readily available aromatic feedstocks to structurally diverse three-dimensional polycyclic molecules make catalytic asymmetric dearomatization reactions of broad interest for both organic synthesis and medicinal chemistry. However, the inherent difficulty for the disruption of aromaticity demands a large energy input during the dearomatization process, which might be incompatible with the conditions generally required by asymmetric catalysis. In this Outlook, we will discuss representative strategies and examples of catalytic asymmetric dearomatization reactions of various aromatic compounds and try to convince readers that by overcoming the above obstacles, catalytic asymmetric dearomatization reactions could advance chemical sciences in many respects.

Asymmetric Hydrogenation of Racemic 6-Aryl 1,4-Dioxaspiro[4.5]decan-7-ones to Functionalized Chiral β-Aryl Cyclohexanols via a Dynamic Kinetic Resolution

A ruthenium-catalyzed asymmetric hydrogenation method for the synthesis of functionalized β-aryl cyclohexanols is described. With chiral spiro ruthenium catalyst (R_a,S,S)-5c, a series of racemic α-aryl cyclohexanones bearing a β-monoethylene ketal group were hydrogenated to the corresponding functionalized β-aryl cyclohexanols in high yields with enantioselectivity of up to 99% ee via a dynamic kinetic resolution. This protocol can be conducted on a decagram scale and provide potential approaches for the synthesis of optically active and densely functionalized aryl cyclohexanols.

Asymmetric Intramolecular Dearomatization of Nonactivated Arenes with Ynamides for Rapid Assembly of Fused Ring System under Silver Catalysis

Arene dearomatization is a straightforward method for converting an aromatic feedstock into functionalized carbocycles. Enantioselective dearomatizations of chemically inert arenes, however, are quite limited and underexplored relative to those of phenols and indoles. We developed a method for diazo-free generation of silver-carbene species from an ynamide and applied it to the dearomatization of nonactivated arenes. Transiently generated norcaradiene could be trapped by intermolecular [4 + 2] cycloaddition, synthesizing polycycles with five consecutive stereogenic centers. This protocol constitutes the first highly enantioselective reaction based on the diazo-free generation of silver-carbene species. Mechanistic investigations revealed a dearomatization followed by two different classes of pericyclic reactions, as well as the origin of the chemo- and enantioselectivity.

Development of a Scalable and Sublimation-Free Route to MTAD

The cyclic azodicarbonyl 4-methyl-1,2,4-triazoline-3,5-dione (MTAD) is a versatile and powerful reagent used mainly in cycloaddition chemistry. Though known for more than 50 years, its unsafe preparation, as well as purification by sublimation, hampered its widespread applicability on a larger scale. Herein we report a scalable and safe route to MTAD, which avoids the generation of methyl isocyanate. Moreover, we demonstrate that sublimation can be circumvented by the application of judicious oxidation conditions, followed by simple filtration. Overall, up to 25 g of MTAD was prepared in a single batch from commercial starting materials in three steps, with recrystallization serving as the only purification in the sequence. When employed in dearomative methodologies, the MTAD obtained by this protocol displayed synthetic efficiency equivalent to that of MTAD purified by sublimation.

Total synthesis of endiandric acid J and beilcyclone A from cyclooctatetraene

The endiandric acids are classic targets in natural product synthesis. The spectacular 8π/6π-electrocylisation/intramolecular Diels-Alder (8π/6π/IMDA) reaction cascade at the heart of their biosynthesis has inspired practitioners and students of pericyclic chemistry for nearly forty years. All previous synthetic approaches have sought to prepare a linear tetraene and thereby initiate the cascade. In this communication we demonstrate the use of cyclooctatetraene to rapidly intercept the 8π/6π/IMDA cascade at the cyclooctatriene stage. Endiandric acid J and beilcyclone A are prepared for the first time in six and five steps, respectively. The strategy features a tactical overall anti-vicinal difunctionalisation of cyclooctatetraene through SN2' alkylation of cyclooctatetraene oxide followed by an intriguing tandem Claisen rearrangement/6π-electrocyclisation from the corresponding vinyl ether. This rapidly constructs an advanced bicyclo[4.2.0]octadiene aldehyde intermediate. Olefinations and intramolecular Diels-Alder cycloadditions complete the syntheses. This establishes a short and efficient new path to the endiandric acid natural products. DFT modelling predicts thermal racemisation of bicyclo[4.2.0]octadiene intermediates, dashing hopes of enantioselective synthesis.

Shaping Molecular Landscapes: Recent Advances, Opportunities, and Challenges in Dearomatization

Dearomatization is a fundamental chemical transformation, and it underlies some of the most efficient tactics for generating three-dimensional complexity from basic two-dimensional precursors. The dearomative toolbox, once restricted to only a handful of reactions, has begun to grow more sophisticated as novel methods are added, introducing more functionality under milder conditions and with more control over chemo-, regio-, and stereoselectivity than ever before. Over the past two decades, major developments in dearomative processes have bolstered significant total-synthesis endeavors and greatly expanded the scope and complexity of chemical building blocks accessible from feedstock arenes. In this Perspective, we highlight some of the recent advances and key challenges that remain in this vibrant area of organic chemistry.

Narciclasine, an isocarbostyril alkaloid, has preferential activity against primary effusion lymphoma

Primary effusion lymphoma (PEL) is a subtype of non-Hodgkin lymphoma associated with infection by Kaposi sarcoma-associated herpes virus (KSHV). PEL is an aggressive disease with extremely poor prognosis when treated with conventional chemotherapy. Narciclasine, a natural product present in Amaryllidaceae family of flowering plants including daffodils, belongs to a class of molecules termed ‘isocarbostyril alkaloid’. We have found that narciclasine displays preferential cytotoxicity towards PEL at low nanomolar concentrations and is approximately 10 and 100-fold more potent than its structural analogs lycoricidine and lycorine, respectively. Narciclasine arrested cell-cycle progression at the G₁ phase and induced apoptosis in PEL, which is accompanied by activation of caspase-3/7, cleavage of PARP and increase in the surface expression of Annexin-V. Although narciclasine treatment resulted in a marked decrease in the expression of MYC and its direct target genes,time-course experiments revealed that MYC is not a direct target of narciclasine. Narciclasine treatment neither induces the expression of KSHV-RTA/ORF50 nor the production of infectious KSHV virions in PEL. Finally, narciclasine provides dramatic survival advantages to mice in two distinct mouse xenograft models of PEL. In conclusion, our results suggest that narciclasine could be a promising agent for the treatment of PEL.

Directed Biosynthesis of Iso-aclacinomycins with Improved Anticancer Activity

A four-enzyme catalyzed hydroxy regioisomerization of anthracycline was integrated into the biosynthetic pathway of aclacinomycin A (ALM-A), to generate a series of iso-ALMs via directed combinatorial biosynthesis combined with precursor-directed mutasynthesis. Most of the newly acquired iso-ALMs exhibit obviously (1-5-fold) improved antitumor activity. Therefore, we not only developed iso-ALMs with potential as clinical drugs but also demonstrated the utility of this tailoring tool for modification of anthracycline antibiotics in drug discovery and development.

N-Heterocyclic carbene (NHC)-catalyzed tandem imine umpolung–aza-Michael addition–oxidation of β-carboline cyclic imines

N-Heterocyclic carbene (NHC)-catalyzed tandem imine umpolung–aza-Michael addition–oxidation of cyclic imines for the synthesis of a wide range of biologically relevant β-carboline-1-one derivatives has been disclosed.

An efficient synthesis of chloro-aminocyclooctanediol and aminocyclooctanetriol: an unexpected acetolysis product

A concise and efficient synthesis of 2-amino-4-chlorocyclooctanediol, aminocyclooctanetriols and unusual 1,3-hydride shift during the ring opening reaction of epoxide is described.

Reversal of reaction type selectivity by Lewis acid coordination: the ortho photocycloaddition of 1- and 2-naphthaldehyde

Lewis acids, such as AlBr₃, completely alter the photochemical behaviour of naphthaldehydes. Instead of typical carbonyl photochemistry, the aldehydes undergo cycloaddition reactions at the arene core upon visible-light irradiation.

The value of a specific substrate class for synthetic applications is greatly enhanced if different types of reactions can be performed selectively upon a judicious choice of reaction conditions. In the present study it was shown that the typical photochemical behaviour of naphthaldehydes is completely altered in the presence of Lewis acids. Without Lewis acids, reactions at the carbonyl group are exclusively observed while Lewis acids facilitate a visible light-mediated cycloaddition at the arene core providing access to products of aromatic C–H functionalization via cyclobutane intermediates.

Visible-Light-Induced Dearomatizations

The dearomatization of aromatic compounds is an important synthetic strategy used in accessing complex three-dimensional structures from simple aromatic precursors. This minireview aims to provide an overview of recent advancements in this area, with a specific focus on visible-light-mediated dearomative transformations. Compared to the conventional high-energy ultraviolet (UV) light-promoted processes, not only these new approaches offer milder reaction conditions to accommodate wider variety of substrates with sensitive functionalities, but also enable the use of photocatalysts and other promoters, significantly expanding the reaction space. Application of these transformations to the synthesis of bioactive compounds are also discussed.

Total Synthesis of (+)-Lycoricidine and Conduramine B-1, ent-C-1, C-4, D-1, ent-F-1, and ent-F-4, and Formal Synthesis of (-)-Laminitol: a C2-Symmetric Chiral-Pool-Based Flexible Strategy

A facile and diversity-oriented synthetic strategy toward aminocyclitol natural products from inexpensive C₂-symmetric l-tartaric acid was developed. The pivotal epoxide was used as a common intermediate to accomplish eight diverse target molecules in six to eleven steps. Various allyl-amine-type conduramines were synthesized in a diastereoselective manner. Heck arylation was explored to construct a phenanthridone ring in a concise synthesis of (+)-lycoricidine. In addition, a highly efficient formal synthesis of (-)-laminitol was developed.