Natural product syntheses via carbonylative cyclizations

Stereo-Differentiating Asymmetric Rh(I)-Catalyzed Pauson-Khand Reaction: A DFT-Informed Approach to Thapsigargin Stereoisomers

We report a stereo-differentiating dynamic kinetic asymmetric Rh(I)-catalyzed Pauson-Khand reaction, which provides access to an array of thapsigargin stereoisomers. Using catalyst-control, a consistent stereochemical outcome is achieved at C2─for both matched and mismatched cases─regardless of the allene-yne C8 stereochemistry. The stereochemical configuration for all stereoisomers was assigned by comparing experimental vibrational circular dichroism (VCD) and 13C NMR to DFT-computed spectra. DFT calculations of the transition-state structures corroborate experimentally observed stereoselectivity and identify key stabilizing and destabilizing interactions between the chiral ligand and allene-yne PKR substrates. The robust nature of our catalyst-ligand system places the total synthesis of thapsigargin and its stereoisomeric analogues within reach.

Total Synthesis of Euphorbialoid A

Euphorbialoid A (1) belongs to the rare diterpenoid family of premyrsinanes and exhibits potent anti-inflammatory effects. The 5/7/6/3-membered carbocycle (ABCD-ring) of 1 contains 11 contiguous stereocenters and seven oxygen-containing functional groups. Moreover, four of the six hydroxy groups of 1 are concentrated in the southern sector and flanked by four structurally different acyl groups. The dense array of various functional groups with disparate reactivities on the tetracyclic ABCD-ring presents a daunting challenge for the chemical synthesis of 1. As a reflection of its formidable complexity, synthesis of 1 or any other premyrsinane diterpenoids has not yet been reported. Here, we devised a novel strategy comprising two stages and achieved the first total synthesis of 1 (35 steps as the longest linear sequence). In the first stage, the ABCD-ring was expeditiously assembled by integrating three powerful transformations: (1) Pt-doped TiO2-catalyzed radical coupling to attach a northern chain to a 6/3-membered CD-ring, (2) Pd-catalyzed decarboxylative asymmetric allylation to construct a quaternary carbon with a southern chain, and (3) a Co-mediated Pauson-Khand reaction to cyclize the two chains into the 5/7-membered AB-ring. In the second stage, three-dimensional structures of the ABCD-ring intermediates were utilized to stereoselectively fabricate the A-ring and site-selectively append the four different acyl groups. In the present total synthesis, we revealed the significance of orchestrating the multistep reaction sequence and incorporating cyclic protective groups. The overall strategy and tactics provide new insights into designing synthetic routes to premyrsinanes and densely oxygenated terpenoids decorated with diverse acyl groups.

Ten-Step Total Synthesis of (±)-Phaeocaulisin A Enabled by Cyclopropanol Ring-Opening Carbonylation

We report an efficient total synthesis of (±)-phaeocaulisin A, a guaianolide sesquiterpene natural product possessing a complex tetracyclic skeleton embedded with an oxaspirolactone and a fused bicyclic lactone, four oxygen-containing stereocenters, and an 8-oxabicyclo[3.2.1]octane core. Our synthesis features a novel palladium-catalyzed cyclopropanol ring-opening carbonylation to access a key γ-ketoester, a chemo- and stereoselective aldol cyclization to form the seven-membered carbocycle, and a cascade ketalization-lactonization to construct the desired tetracyclic skeleton. With these strategically important C-C and C-O bond formation transformations, a 10-step total synthesis of (±)-phaeocaulisin A was achieved. We further developed the cyclopropanol ring-opening carbonylation chemistry to provide an alternative approach to prepare γ-ketoesters. Biologically, the penultimate intermediate with an α-methylene γ-butyrolactone moiety was identified as a promising lead compound with anticancer proliferation activity against a panel of triple-negative or HER2+ breast cancer cell lines.

Systematic Parameter Determination Aimed at a Catalyst-Controlled Asymmetric Rh(I)-Catalyzed Pauson-Khand Reaction

Transition metal-catalyzed carbocyclization reactions have revolutionized the synthesis of complex cyclic organic compounds. Yet, subtle substrate changes can significantly alter reaction pathways. The asymmetric Rh(I)-catalyzed Pauson-Khand reaction (PKR) exemplifies such a reaction, hindered by a narrow substrate scope and competing reactivity modes. In this study, we identified parameters predictive of the yield and enantioselectivity in the catalyst-controlled asymmetric PKR, using 1,6-enynes with a 2,2-disubstituted alkene. In this way, ring-fused cyclopentenones can be formed with chiral quaternary carbon centers. Using bisphosphine ligand parameters from palladium complexes, including the energy of the Pd lone pair orbital and the angle formed by the phosphorus aryl groups on the ligand, we established strong correlations with experimental ln(er) (R 2 = 0.99 and 0.91) for two distinct precursors. Solvent dipole moments correlated with ln(er) for high-dipole-moment precursors (R 2 = 0.94), while Abraham's hydrogen bond basicity is more relevant for low-dipole-moment precursors (R 2 = 0.93). Additionally, counterions were found to have a significant impact on the PKR reactivity and selectivity, as does the steric demand of the alkyne substituent of the enyne precursor. In the latter case, ln(er) correlates with Sterimol B1 values for products from different alkyne substituents (R 2 = 0.99). Furthermore, the computed C≡C wavenumber of the enyne precursor can be directly aligned with the yield of asymmetric PKRs.

Gold-Catalyzed Alkoxy-Carbonylation of Aryl and Vinyl Iodides

Herein, for the first time, we disclose the gold-catalyzed alkoxy-carbonylation of aryl and vinyl iodides utilizing ligand-enabled Au(I)/Au(III) redox catalysis. The present methodology is found to be general, efficient, employs mild reaction conditions and showcases a broad substrate scope even with structurally complex molecules. Density functional theory (DFT) calculations revealed mechanistic pathways distinct from those of conventional transition metal-catalyzed carbonylation reactions.

Direct synthesis of dialkyl ketones from deoxygenative cross-coupling of carboxylic acids and alcohols

Carboxylic acids and alcohols are widely commercially available, structurally diverse, benchtop stable, and ubiquitous in both natural products and pharmaceutical agents, making them ideal coupling partners for organic synthesis. Though various transformations have been developed by enabling the activation and subsequent cross-coupling of carboxylic acids and alcohols in separate contexts, the direct coupling of these two structural motifs to build value-added molecules is rare. Herein, we developed a direct deoxygenative cross-coupling between carboxylic acids and alcohols for dialkyl ketone synthesis via photoredox/nickel dual catalysis. This protocol provides a powerful platform to construct a wide range of structurally diverse ketone scaffolds with broad substrate scope, good functional group tolerance, step-economy and mild reaction conditions, using simple and readily available substrates. Moreover, the large-scale synthesis and late-stage functionalization of biological molecules also demonstrate the potential practicality.

Palladium-Catalyzed Asymmetric Tandem Carbonylation-Heck Reaction of Cyclopentenes to Access Chiral Bicyclo[3.2.1]octenes

A palladium-catalyzed asymmetric tandem carbonylation-Heck reaction of cyclopentenes with carbon monoxide (CO) has been disclosed. This desymmetrization procedure afforded a series of bicyclo[3.2.1]octenes with one chiral quaternary and one tertiary carbon center in good yields with good enantioselectivities. This reaction proceeds via an acyl-palladium intermediate, followed by migratory insertion of the alkenes.

Synthesis of a collection of nootkatone analogues with diverse skeletons

A collection of ring distorted analogue of Nootkatone including 6 CTD (Complex to Diversity) compounds and 9 SAR (Structure Activity Relationship) compounds were synthesized utilizing the carbonyl group as a starting reaction point.

Probing the Mechanism of Ni-Catalyzed Asymmetric Reppe Carbonylation of Cyclopropenes with CO and ROH

There is ongoing intense interest in catalysis with the Earth-abundant metal nickel. This DFT study reveals a plausible mechanism for the first Ni-catalyzed asymmetric Reppe carbonylation of cyclopropenes with carbon monoxide and phenols/alcohols. The RO-H bond undergoes a distinct heterolytic cleavage rather than the proposed oxidative addition, transferring a proton to a nickel-bound anionic carbon atom in a stereoselective manner. This and other novel insights gained can have implications for developing new asymmetric Reppe reactions.

Synthesis of Stereodefined Enones from the Cross-Electrophile Coupling of Activated Acrylic Acids with Alkyl Bromides

We report a one-pot synthesis of (E)-trisubstituted enones from acrylic acids through the in situ generation of a 2-pyridyl ester and subsequent cross-electrophile coupling with a nickel catalyst under reducing conditions. The scope of trisubstituted enones is broad and compatible with functionality that can be challenging in established olefination techniques. We highlight conditions necessary to suppress undesired side reactions from the α,β-unsaturated carbonyl and improve cross-electrophile coupling approaches to prepare enones.

Recent advances in the total synthesis of galantamine, a natural medicine for Alzheimer's disease

Covering: 2006 to 2023(-)-Galantamine is a natural product with distinctive structural features and potent inhibitory activity against acetylcholine esterase (AChE). It is clinically approved for the treatment of Alzheimer's disease. The clinical significance and scarcity of this natural product have prompted extensive and ongoing efforts towards the chemical synthesis of this challenging tetracyclic structure. The objective of this review is to summarize and discuss recent progress in the total synthesis of galantamine from 2006 to 2023. The contents are organized according to the synthetic strategies for the construction of the quaternary center. Key features of each synthesis have been highlighted, followed by a summary and outlook at the end.

Palladium-Catalyzed Cascade Carbonylation Reaction: Synthesis of Fused Isoindolinones

A palladium-catalyzed cascade carbonylation reaction of 2-bromo-N-(2-iodophenyl)benzamides with benzylidenecyclopropanes for the synthesis of fused isoindolinone derivatives has been developed. A broad range of 6/5/6/6 tetracyclic isoindolinone products were efficiently prepared in moderate to good yields with diverse substitution. Two carbonyl groups were incorporated into the substrates in a single step with the formation of four carbon-carbon bonds and two carbon-heteroatom bonds.

A divergent intermediate strategy yields biologically diverse pseudo-natural products

The efficient exploration of biologically relevant chemical space is essential for the discovery of bioactive compounds. A molecular design principle that possesses both biological relevance and structural diversity may more efficiently lead to compound collections that are enriched in diverse bioactivities. Here the diverse pseudo-natural product (PNP) strategy, which combines the biological relevance of the PNP concept with synthetic diversification strategies from diversity-oriented synthesis, is reported. A diverse PNP collection was synthesized from a common divergent intermediate through developed indole dearomatization methodologies to afford three-dimensional molecular frameworks that could be further diversified via intramolecular coupling and/or carbon monoxide insertion. In total, 154 PNPs were synthesized representing eight different classes. Cheminformatic analyses showed that the PNPs are structurally diverse between classes. Biological investigations revealed the extent of diverse bioactivity enrichment of the collection in which four inhibitors of Hedgehog signalling, DNA synthesis, de novo pyrimidine biosynthesis and tubulin polymerization were identified from four different PNP classes.

Competing Mechanisms in Palladium-Catalyzed Alkoxycarbonylation of Styrene

Palladium-catalyzed carbonylation is a versatile method for the synthesis of various aldehydes, esters, lactones, or lactams. Alkoxycarbonylation of alkenes with carbon monoxide and alcohol produces either saturated or unsaturated esters as a result of two distinct catalytic cycles. The existing literature presents an inconsistent account of the procedures favoring oxidative carbonylation products. In this study, we have monitored the intermediates featured in both catalytic cycles of the methoxycarbonylation of styrene PhCH=CH2 as a model substrate, including all short-lived intermediates, using mass spectrometry. Comparing the reaction kinetics of the intermediates in both cycles in the same reaction mixture shows that the reaction proceeding via alkoxy intermediate [PdII]-OR, which gives rise to the unsaturated product PhCH=CHCO2Me, is faster. However, with an advancing reaction time, the gradually changing reaction conditions begin to favor the catalytic cycle dominated by palladium hydride [PdII]-H and alkyl intermediates, affording the saturated products PhCH2CH2CO2Me and PhCH(CO2Me)CH3 preferentially. The role of the oxidant proved to be crucial: using p-benzoquinone results in a gradual decrease of the pH during the reaction, swaying the system from oxidative conditions toward the palladium hydride cycle. By contrast, copper(II) acetate as an oxidant guards the pH within the 5-7 range and facilitates the formation of the alkoxy palladium complex [PdII]-OR, which favors the oxidative reaction producing PhCH=CHCO2Me with high selectivity. Hence, it is the oxidant, rather than the catalyst, that controls the reaction outcome by a mechanistic switch. Unraveling these principles broadens the scope for developing alkoxycarbonylation reactions and their application in organic synthesis.

From Conventional to Sustainable Catalytic Approaches for Heterocycles Synthesis

Synthesis of heterocyclic compounds is fundamental for all the research area in chemistry, from drug synthesis to material science. In this framework, catalysed synthetic methods are of great interest to effective reach such important building blocks. In this review, we will report on some selected examples from the last five years, of the major improvement in the field, focusing on the most important conventional catalytic systems, such as transition metals, organocatalysts, to more sustainable ones such as photocatalysts, iodine-catalysed reaction, electrochemical reactions and green innovative methods.

Palladium-Catalyzed Carbonylative Difunctionalization of Unactivated Alkenes Initiated by Unstabilized Enolates

This report describes the first example of palladium-catalyzed carbonylative difunctionalization of unactivated alkenes initiated by enolate nucleophiles. The approach involves initiation by an unstabilized enolate nucleophile under an atmospheric pressure of CO and termination with a carbon electrophile. This process is compatible with a diverse range of electrophiles, including aryl, heteroaryl, and vinyl iodides to yield synthetically useful 1,5-diketone products, which were demonstrated to be precursors for multi-substituted pyridines. A PdI -dimer complex with two bridging CO units was observed although its role in catalysis is not yet understood.

Palladium Iodide Catalyzed Multicomponent Carbonylative Synthesis of 2-(4-Acylfuran-2-yl)acetamides

2-Propargyl-1,3-dicarbonyl compounds have been carbonylated under oxidative conditions and with the catalysis of the PdI2/KI catalytic system to selectively afford previously unreported 2-(4-acylfuran-2-yl)acetamides in fair to good yields (54-81%) over 19 examples. The process takes place under relatively mild conditions and occurs via a mechanistic pathway involving Csp-H activation by oxidative monoamincarbonylation of the terminal triple bond of the substrates with formation of 2-ynamide intermediates, followed by 5-exo-dig O-cyclization (via intramolecular conjugate addition of the in situ formed enolate to the 2-ynamide moiety) and aromative isomerization.

Reductive Aza-Pauson-Khand Reaction of Nitriles

γ-Lactams are valuable heterocycles in synthetic chemistry and drug development. Here, we report a reductive aza-Pauson-Khand reaction (aza-PKR) of an alkyne, a nitrile, and Co₂(CO)₈. A wide array of bicyclic α,β-unsaturated γ-lactams containing two adjacent stereocenters, including an all-carbon quaternary center, from alkyne-tethered malononitriles are efficiently accessed in high diastereoselectivity. Preliminary mechanistic investigations by experiments and DFT calculations reveal that the reaction undergoes an aza-PKR process followed by a in situ reduction. The reducing reagent generated in situ from water also provides a practical tool for deuterium incorporation into the γ-position of lactams using D₂O as the deuterium source. This study represents a new mode for [2 + 2 + 1] cycloaddition that enables the direct use of nitrile in aza-heterocycle synthesis.

Palladium-Catalyzed Carbonylations: Application in Complex Natural Product Total Synthesis and Recent Developments

Carbon monoxide is a cheap and abundant C1 building block that can be readily incorporated into organic molecules to rapidly build structural complexity. In this Perspective, we outline several recent (since 2015) examples of palladium-catalyzed carbonylations in streamlining complex natural product total synthesis and highlight the strategic importance of these carbonylation reactions in the corresponding synthesis. The selected examples include spinosyn A, callyspongiolide, perseanol, schizozygane alkaloids, cephanolides, and bisdehydroneostemoninine and related stemona alkaloids. We also provide our perspective about the recent advancements and future developments of palladium-catalyzed carbonylations.

Pd-Catalyzed Asymmetric 5-exo-trig Cyclization/Cyclopropanation/Carbonylation of 1,6-Enynes for the Construction of Chiral 3-Azabicyclo[3.1.0]hexanes

We herein disclose a mild and efficient access to chiral 3-azabicyclo[3.1.0]hexanes via a Pd-catalyzed asymmetric 5-exo-trig cyclization/cyclopropanation/carbonylation of 1,6-enynes. Various nucleophiles, such as alcohols, phenols, amines and water, are well compatible with the reaction system. This reaction forms three C-C bonds, two rings, two adjacent quaternary carbon stereocenters as well as one C-O/C-N bond with excellent regio- and enantioselectivities. The products could be further functionalized to generate a library of 3-azabicyclo[3.1.0]hexane frameworks.

Palladium-catalyzed generation of CO from formic acid for alkoxycarbonylation of internal alkenes involves a PTSA-assisted NH-Pd mechanism: a DFT mechanistic study

DFT calculations have been performed to find the mechanism of the alkyloxycarbonylation of an internal alkene with HCOOH catalyzed by a palladium complex with P,N hemilabile ligands. Four different cycles have been explored in detail, and a plausible catalytic cycle involves the decomposition of HCOOH/HCOOMe to CO, internal alkene isomerization, terminal alkene insertion, CO migratory insertion and methanolysis. It is shown that decomposition and isomerization processes involve a cooperative P,N hemilabile ligand and Pd(0) (NH-Pd) rather than the Pd(II) hydride (Pd-H) mechanism. Intriguingly, the simultaneous presence of PTSA acts as a hydrogen shuttle (H-shuttle), assisting CO generation and methanolysis. With such a mechanism, the rate-determining transition state corresponds to internal alkene isomerization, which is consistent with the experimental observation that isomerization was the slow step in this process. The back-bonding between palladium and olefin and rapid hydrogen transfer in the presence of a PTSA H-shuttle are responsible for the moderate barriers. In addition, a careful study of the solvent effect indicates that polar solvents, which are capable of hydrogen bonding, can promote the catalytic reactions. Mechanistic insights gained by this theoretical study have not only rationalized the experimental observations well but also have implications for new reaction development.

Rhodium-catalyzed aminoacylation of alkenes via carbonylative C–H activation toward poly(hetero)cyclic alkylarylketones

This work discloses the facile construction of polyheterocyclic alkylarylketones by the rhodium-catalyzed carbonylative aminoacylation of alkenes involving C–H activation, which provides molecules as candidates for the screening of antitumor agents.

Ring contraction in synthesis of functionalized carbocycles

Carbocycles are a key and widely present structural motif in organic compounds. The construction of structurally intriguing carbocycles, such as highly-strained fused rings, spirocycles or highly-functionalized carbocycles with congested stereocenters, remains challenging in organic chemistry. Cyclopropanes, cyclobutanes and cyclopentanes within such carbocycles can be synthesized through ring contraction. These ring contractions involve re-arrangement of and/or small molecule extrusion from a parental ring, which is either a carbocycle or a heterocycle of larger size. This review provides an overview of synthetic methods for ring contractions to form cyclopropanes, cyclobutanes and cyclopentanes en route to structurally intriguing carbocycles.

Non-Noble Metal-Catalyzed Carbonylative Multi-Component Reactions

Carbonylative multi-component reactions (CMCR), having four or more kinds of starting materials, provide an efficient strategy for the preparation of polyfunctional carbonylated compounds. Diverse CMCR utilizing non-noble transition-metal catalysts have been developed. This review summarized and discussed the recent advances in non-noble metal-catalyzed carbonylative multi-component reactions.

Synthesis of Benzothiophene-3-carboxylic Esters by Palladium Iodide-Catalyzed Oxidative Cyclization-Deprotection-Alkoxycarbonylation Sequence under Aerobic Conditions

A palladium-catalyzed carbonylative approach to benzothiophene-3-carboxylic esters, starting from simple and readily available building blocks [2-(methylthio)phenylacetylenes, CO, an alcohol, and O₂ (from air)], is reported. The process is catalyzed by the simple PdI₂/KI catalytic system to give the desired products in fair to high yields (57-83%). Interestingly, the reaction also works nicely in the ionic liquid BmimBF₄ as the solvent, with the possibility to recycle the catalytic system several times without appreciable loss of activity.

Palladium-Catalyzed Asymmetric Dearomative Carbonylation of Indoles

Herein, we disclose a strategy for the asymmetric dearomatization of N-arylacyl indoles via a palladium-catalyzed tandem Heck/carbonylation, leading to an array of indoline-3-carboxylates bearing vicinal C2-aza-quaternary and C3 tertiary stereocenters in high yields and excellent enantio- and diastereoselectivities. This study is an important advance in the field of asymmetric carbonylation and enantioselective dearomatization reactions.

Palladium-Catalyzed Carbonylation of Disulfides and Ethylene: Synthesis of β-Thiopropionate Thioesters

Transforming carbon monoxide (C1) and ethylene (C2) into high value-added chemicals is of great significance from an economic perspective, especially to multifunctionalized C3 compounds. Herein, we developed a palladium-catalyzed thiocarbonylative 1,2-difunctionalization of ethylene. Employing NiXantPhos as the ligand and DCE as the solvent, a series of organic disulfides can be successfully transformed into β-thiopropionate thioesters in good yields.

Palladium-Catalyzed Carbonylative Sonogashira/Annulation Reaction: Synthesis of Indolo[1,2-b]isoquinolines

A palladium-catalyzed carbonylative Sonogashira/annulation reaction for the synthesis of indolo[1,2-b]isoquinolines has been developed. Tetracyclic 6/5/6/6 indoline skeletons were synthesized in moderate to good yields from easily available 2-bromo-N-(2-iodophenyl)benzamides and terminal alkynes. Notably, this efficient methodology established three C-C bonds and a C-N bond through a one-step transformation and provided a new method for the synthesis of indolo[1,2-b]isoquinoline derivatives.

Synthesis of unprotected glyco-alkynones via molybdenum-catalyzed carbonylative Sonogashira cross-coupling reaction

Herein we report a novel Mo-catalyzed carbonylative Sonogashira cross-coupling between 2-iodoglycals and terminal alkynes. The reaction displays major improvements compared to a related Pd-catalyzed procedure previously published by our group, such as utilizing unprotected sugar derivatives as starting materials and tolerance to substrates bearing chelating groups. In this work we also demonstrate the utility of the glyco-alkynone products as platform for further functionalization by synthesizing glyco-flavones via Au-catalyzed 6-endo-dig cyclization.

Palladium-catalyzed enantioselective carbonylation reactions

Carbonylation, one of the most powerful approaches to the preparation of carbonylated compounds, has received significant attention from researchers active in various fields. Indeed, impressive progress has been made on this subject over the past few decades. Among the various types of carbonylation reactions, asymmetric carbonylation is a straightforward methodology for constructing chiral compounds. Although rhodium-catalyzed enantioselective hydroformylations have been discussed in several elegant reviews, a general review on palladium-catalyzed asymmetric carbonylations is still missing. In this review, we summarize and discuss recent achievements in palladium-catalyzed asymmetric carbonylation reactions. Notably, this review’s contents are categorized by reaction type.

Palladium-catalyzed tandem Heck/carbonylation/aminocarbonylation en route to chiral heterocyclic α-ketoamides

An unprecedented tandem carbonylation/aminocarbonylation triggered by palladium-catalyzed enantioselective Heck-type exocyclopalladation delivering chiral heterocyclic α-ketoamides has been developed.

One-pot synthesis of benzo[b][1,4]diazepines via carbonylative Sonogashira reaction and aza-Michael addition cyclocondensation

The benzodiazepines are essential structural motifs commonly found in biologically active compounds and pharmaceutical agents. The general and step-economy methods for the direct synthesis of the benzodiazepines from simple and...

Cooperative Cu/Pd-catalyzed borocarbonylation of ethylene

A general procedure for the synthesize of β-boryl ketones enabled by cooperative Cu/Pd-catalyzed borocarbonylation of ethylene has been developed.

Diastereoselective Alkene Hydroesterification Enabling the Synthesis of Chiral Fused Bicyclic Lactones

Palladium-catalysed diastereoselective hydroesterification of alkenes assisted by the coordinative hydroxyl group in the substrate afforded a variety of chiral γ-butyrolactones bearing two stereocenters. Employing the carbonylation-lactonization products as the key intermediates, the route from the alkenes with single chiral center to chiral THF-fused bicyclic γ-lactones containing three stereocenters was developed.

Total Syntheses of Galanthamine and Lycoramine via a Palladium-Catalyzed Cascade Cyclization and Late-Stage Reorganization of the Cyclized Skeleton

Herein, we report the highly efficient total syntheses of galanthamine and lycoramine from a common tetracyclic intermediate. This concise synthetic route features a two-phase strategy, which includes the early-stage rapid construction of a tetracyclic skeleton followed by the late-stage selective reorganization of the tetracyclic skeleton. Key to the success of this strategy are a palladium-catalyzed carbonylative cascade annulation, a DDQ-mediated intramolecular regioselective oxidative lactamization, as well as a BF₃·Et₂O-promoted reorganization of the bridged tetracyclic skeleton.

Highly Regio- and Diastereoselective Tethered Aza-Wacker Cyclizations of Alkenyl Phosphoramidates

We present highly diastereoselective tethered aza-Wacker cyclization reactions of alkenyl phosphoramidates. "Arming" the phosphoramidate tether with 5-chloro-8-quinolinol was essential to achieving >20:1 diastereoselectivity in these reactions. The substrate scope with respect to alkenyl alcohols and phosphoramidate tether was extensively explored. The scalability of the oxidative cyclization was demonstrated, and the product cyclophosphoramidates were shown to be valuable synthons, including for tether removal. With chiral alkenyl precursors, enantiopure cyclic phosphoramidates were formed.

Transition-metal-catalyzed C-H bond activation/functionalization and annulation of phthalazinones

Phthalazinones and their higher congeners are commonly prevalent structural motifs that occur in natural products, bioactive molecules, and pharmaceuticals. In the past few decades, transition-metal-catalyzed reactions have received an overwhelming response from organic chemists as challenging organics and heterocycles could be built with ease. Currently, the synthesis of phthalazinones largely depends on transition-metal catalysis, especially by palladium-catalyzed carbonylation. Further, the dominance of transition-metal catalysts was realized from the phthalazinones viewpoint, as nitrogen and oxygen atoms endowed upon them act as directing groups to facilitate diverse C-H activation/functionalization/annulation reactions. This highlight describes the various synthetic methods used to access phthalazinones and functionalize them by reacting with various coupling partners via chelation assistance strategy involving C(sp²)-H/N-H bond activation in the presence of transition-metal (Rh, Ru, Pd, and Ir) catalysts. The mechanisms of sulfonylation, halogenation, acylmethylation, alkylation, and annulation reactions are discussed.

A general strategy for the synthesis of α-trifluoromethyl- and α-perfluoroalkyl-β-lactams via palladium-catalyzed carbonylation

β-Lactam compounds play a key role in medicinal chemistry, specifically as the most important class of antibiotics. Here, we report a novel one-step approach for the synthesis of α-(trifluoromethyl)-β-lactams and related products from fluorinated olefins, anilines and CO. Utilization of an advanced palladium catalyst system with the Ruphos ligand allows for selective cycloaminocarbonylations to give diverse fluorinated β-lactams in high yields.

Iridium-catalyzed stereoselective [3+2] annulation of α-oxocarboxylic acids with 1,3-dienes

The stereoselective annulation of α-oxocarboxylic acids with 1,3-dienes proceeded in the presence of a hydroxoiridium catalyst to give α-hydroxy-γ-lactones in good yields with high 3,5-trans relative stereochemistry. The use of a chiral diene ligand for a cationic iridium complex enabled asymmetric annulation with high enantioselectivity.

Palladium-Catalyzed Three-Component Coupling Reaction via Benzylpalladium Intermediate

Transition-metal catalyzed multi-component reactions have captured the attention of researchers in organic synthesis and drug synthesis due to their advantages of simple operation, easy availability of raw materials and without separation of intermediates. Among the multi-component reactions, the three-component processes have been developed into effective organic procedures. This personal account reviews our and other group's studies on the development of three-component coupling reaction for the rapid construction of two new chemical bonds simultaneously via benzylpalladium intermediates. Catalyst-switched three-component reactions of benzyl halides, activated olefins, and allyltributylstannane were successfully conducted to produce the corresponding benzylallylation products. Activation and conversion of carbon monoxide and carbon dioxide via π-benzylpalladium intermediates provide access to a wide range of unsaturated ketones and esters with excellent functional group tolerance. Meanwhile, other methods to produce benzylpalladium intermediates, including Heck insertion of alkenes into arylpalladium complexes, the oxidative addition of benzyl carbonate to palladium complexes and palladium-carbene migratory insertion, were also highlighted.

The Discovery of Two Novel Classes of 5,5-Bicyclic Nucleoside-Derived PRMT5 Inhibitors for the Treatment of Cancer

Protein arginine methyltransferase 5 (PRMT5) is a type II arginine methyltransferase that catalyzes the post-translational symmetric dimethylation of protein substrates. PRMT5 plays a critical role in regulating biological processes including transcription, cell cycle progression, RNA splicing, and DNA repair. As such, dysregulation of PRMT5 activity is implicated in the development and progression of multiple cancers and is a target of growing clinical interest. Described herein are the structure-based drug designs, robust synthetic efforts, and lead optimization strategies toward the identification of two novel 5,5-fused bicyclic nucleoside-derived classes of potent and efficacious PRMT5 inhibitors. Utilization of compound docking and strain energy calculations inspired novel designs, and the development of flexible synthetic approaches enabled access to complex chemotypes with five contiguous stereocenters. Additional efforts in balancing bioavailability, solubility, potency, and CYP3A4 inhibition led to the identification of diverse lead compounds with favorable profiles, promising in vivo activity, and low human dose projections.