Efficient Enantioselective Syntheses of (+)-Dalesconol A and B

Electrophile-Arene Affinity: An Energy Scale for Evaluating the Thermodynamics of Electrophilic Dearomatization Reactions

Rational design and development of organic reactions are lofty goals in synthetic chemistry. Quantitative description of the properties of molecules and reactions by physical organic parameters plays an important role in this regard. In this Article, we report an energy scale, namely, electrophile-arene affinity (EAA), for evaluating the thermodynamics of electrophilic dearomatization reactions, a class of important transformations that can rapidly build up molecular complexity and structural diversity by converting planar aromatic compounds into three-dimensional cyclic molecules. The acquisition of EAA data can be readily achieved by theoretically calculating the enthalpy changes (ΔH) of the hypothetical reactions of various (cationic) electrophiles with aromatic systems (taking the 1-methylnaphthalen-2-olate ion as an example in this study). Linear correlations are found between the calculated ΔH values and established physical organic parameters such as the percentage of buried volume %VBur (steric effect), Hammett's σ or Brown's σ+ (electronic effect), and Mayr's E (reaction kinetics). Careful analysis of the ΔH values leads to the rational design of a dearomative alkynylation reaction using alkynyl hypervalent iodonium reagents as the electrophiles.

P-Stereogenic Phosphorus Ligands in Asymmetric Catalysis

Chiral phosphorus ligands play a crucial role in asymmetric catalysis for the efficient synthesis of useful optically active compounds. They are largely categorized into two classes: backbone chirality ligands and P-stereogenic phosphorus ligands. Most of the reported ligands belong to the former class. Privileged ones such as BINAP and DuPhos are frequently employed in a wide range of catalytic asymmetric transformations. In contrast, the latter class of P-stereogenic phosphorus ligands has remained a small family for many years mainly because of their synthetic difficulty. The late 1990s saw the emergence of novel P-stereogenic phosphorus ligands with their superior enantioinduction ability in Rh-catalyzed asymmetric hydrogenation reactions. Since then, numerous P-stereogenic phosphorus ligands have been synthesized and used in catalytic asymmetric reactions. This Review summarizes P-stereogenic phosphorus ligands reported thus far, including their stereochemical and electronic properties that afford high to excellent enantioselectivities. Examples of reactions that use this class of ligands are described together with their applications in the construction of key intermediates for the synthesis of optically active natural products and therapeutic agents. The literature covered dates back to 1968 up until December 2023, centering on studies published in the late 1990s and later years.

Recent advances in Pd-catalyzed asymmetric cyclization reactions

Over the past few decades, there have been major developments in transition metal-catalyzed asymmetric cyclization reactions, enabling the convenient access to a wide spectrum of structurally diverse chiral carbo- and hetero-cycles, common skeletons found in fine chemicals, natural products, pharmaceuticals, agrochemicals, and materials. In particular, a plethora of enantioselective cyclization reactions have been promoted by chiral palladium catalysts owing to their outstanding features. This review aims to collect the latest advancements in enantioselective palladium-catalyzed cyclization reactions over the past eleven years, and it is organized into thirteen sections depending on the different types of transformations involved.

sSPhos: A General Ligand for Enantioselective Arylative Phenol Dearomatization via Electrostatically-Directed Palladium Catalysis

Arylative phenol dearomatization affords complex, cyclohexanone-based scaffolds from simple starting materials, and asymmetric versions allow access to valuable enantioenriched structures. However, bespoke chiral ligands must typically be identified for each new scaffold variation. We have addressed this limitation by applying the concept of electrostatically-directed palladium catalysis whereby the chiral sulfonated ligand sSPhos engages in electrostatic interactions with a phenolate substrate via its associated alkali metal cation. This approach allows access to highly enantioenriched spirocyclohexadienones, a process originally reported by Buchwald and co-workers in a predominantly racemic manner. In addition, sSPhos is proficient at forming two other distinct scaffolds, which had previously required fundamentally different chiral ligands, as well as a novel oxygen-linked scaffold. We envisage that the broad generality displayed by sSPhos will facilitate the expansion of this important reaction type and highlight the potential of this unusual design principle, which harnesses attractive electrostatic interactions.

FeIII -Based Eutectic Mixtures as Multi-task and Reusable Reaction Media for Efficient and Selective Conversion of Alkynes into Carbonyl Compounds

An efficient, simple and general protocol for the selective hydration of terminal alkynes into the corresponding methyl ketones has been developed by using a cheap, easy-to-synthesise and sustainable FeIII -based eutectic mixture [FeCl3  ⋅ 6H2 O/Gly (3 : 1)] as both promoter and solvent for the hydration reaction, working: i) under mild (45 °C) and bench-type reaction conditions (air); and ii) in the absence of ligands, co-catalysts, co-solvents or toxic, non-abundant and expensive noble transition metals (Au, Ru, Pd). When the final methyl ketones are solid/insoluble in the eutectic mixture, the hydration reaction takes place in 30 min, and the obtained methyl ketones can be isolated by simply decanting the liquid FeIII -DES, allowing the direct isolation of the desired ketones without VOC solvents. By using this straightforward and simple isolation protocol, we have been able to recycle the FeIII -based eutectic mixture system up to eight consecutive times. Furthermore, the FeIII -eutectic mixture is able to promote the selective and efficient formal oxidation of internal alkynes into 1,2-diketones, with the possibility of recycling this system up to three consecutive times. Preliminary investigations into a possible mechanism for the oxidation of the internal alkynes seem to indicate that it proceeds through the formation of the corresponding methyl ketones and α-chloroketones.

Synthesis of Spirotricyclic Core of Bonnadiene

We herein describe a new approach for the efficient synthesis of the tricyclic core of diterpene bonnadiene. The synthetically challenging and unusual [6-7-5] spirotricyclic skeleton including the all-carbon quaternary stereocenter, was installed diastereoselectively via a type II [5 + 2] cycloaddition, followed by a unique vinylogous semipinacol rearrangement. The described chemistry demonstrates the feasibility of making the [6-7-5] spirotricyclic skeleton of the final product from the strained bridged [7-8-5] ring system.

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.

Total Synthesis of Dalesconol A by Pd(0)/Norbornene-Catalyzed Three-Fold Domino Reaction and Pd(II)-Catalyzed Trihydroxylation

Herein, we describe a concise total synthesis of dalesconol A through a "polycyclization/oxidation" approach. In the polycyclization stage, a Pd(0)/NBE-catalyzed 3-fold domino reaction and a subsequent intramolecular Michael addition have been utilized for the one-step assembly of the heptacyclic molecular skeleton. In the late stage of oxidation state adjustments, a stepwise sequence including site-selective benzylic oxidation, Pd(II)-catalyzed oxime ether directed trihydroxylation, and desaturation has been adopted to introduce the oxygen functionalities and furnish the synthesis of dalesconol A. With the advantage of the late-stage amidation of three C-H bonds in a single step, the amino analogue of dalesconol A has also been obtained with high efficiency.

Enantioselective Total Synthesis of Cepharatines via Bioinspired Ring Reconstruction

We describe enantioselective total syntheses of cepharatines A-D, members of the hasubanan alkaloid family, which feature an unusual tetracyclic skeleton including an azabicyclo[3.3.1]nonane motif. A key reaction is a regio-divergent oxidative phenolic coupling reaction that affords the tricyclic core structure of hasubanan with different substitution patterns on the A-ring, including the all-carbon quaternary stereogenic center at C13, in a single step. The characteristic tetracyclic azabicyclo[3.3.1]nonane motif was constructed by means of a bioinspired cascade reaction involving the retro-aza-Michael reaction/hemiaminal formation.

Palladium-catalyzed post-Ugi arylative dearomatization/Michael addition cascade towards plicamine analogues

A palladium-catalyzed intramolecular cyclization of Ugi-adducts via a cascade dearomatization/aza-Michael addition process has been developed. Diverse plicamine analogues are constructed in a rapid, highly efficient and step-economical manner, through the combination of an Ugi-4CR and a palladium-catalyzed dearomatization. The synthetic utility of this approach is illustrated by further functional group transformations.

Organocatalytic Asymmetric Arylation of p-Quinone Phosphonates: A Green Access to Biaryl Monophosphorus Ligands

Herein, we report a highly efficient organocatalytic asymmetric synthesis of axially chiral biaryl phosphonates with p-quinone phosphonates and 2-naphthols via CPA-catalyzed asymmetric arylations. A series of chiral biaryl monophosphonates were obtained in excellent yields and enantioselectivities (up to 99% yield and 95% ee). This reaction could be operated at a gram scale with a low catalyst loading (0.5 mol %). Remarkably, our approach provides a green and ready access to chiral biaryl monophosphorus ligands. Compound 4ca was successfully converted to novel chiral biaryl monophosphorus ligands 7a, 7b, and 8 with high enantioselectivities in three steps.

Total synthesis of (+)-spiroindimicin A and congeners unveils their antiparasitic activity

The spiroindimicins are a unique class of chlorinated indole alkaloids characterized by three heteroaromatic rings structured around a congested spirocyclic stereocenter. Here, we report the first total synthesis of (+)-spiroindimicin A, which bears a challenging C-3′/C-5′′-linked spiroindolenine. We detail our initial efforts to effect a biomimetic oxidative spirocyclization from its proposed natural precursor, lynamicin D, and describe how these studies shaped our final abiotic 9-step solution to this complex alkaloid built around a key Pd-catalyzed asymmetric spirocyclization. Scalable access to spiroindimicins A, H, and their congeners has enabled discovery of their activity against several parasites relevant to human health, providing potential starting points for new therapeutics for the neglected tropical diseases leishmaniasis and African sleeping sickness.

Spiroindimicins A and H have been synthesized for the first time via a key palladium-catalyzed spirocyclization. Access to these alkaloids and several congeners has allowed the discovery of their antiparasitic properties.

Ni/AntPohs-Catalyzed Stereoselective Asymmetric Intramolecular Reductive Coupling of N-1,6-Alkynones

An efficient nickel-catalyzed stereoselective asymmetric intramolecular reductive coupling of N-1,6-alkynones is reported. A P-chiral monophosphine ligand AntPhos was found to be a privileged catalyst for constructing versatile functionalized chiral pyrrolidine rings using triethylsilane as the reducing reagent. Concise synthesis of pyrrolidines with chiral tertiary allylic alcohols was achieved in high yields (99%), excellent stereoselectivity (>99:1 E/Z), and enantioselectivity (>99:1 er) with very broad substrate scope. Totally, thirty-five N-1,6-alkynones were synthesized and applied in this reaction successfully. This reaction can be scaled up to gram scale without loss of its enantioselectivity. Ligand effects and reaction mechanism are investigated in detail. While the developed asymmetric synthesis of pyrrolidine with chiral tertiary allylic alcohols is anticipated to find wider applications in organic synthesis and chemical biology, the discovered new reactions of N-1,6-alkynone with AntPhos using different catalyst systems would further expanded its new research fields and attract more detailed explorations in the future.

Recent advances in total syntheses of natural products containing the benzocycloheptane motif

Covering: 2010 to 2020Benzocycloheptane is a fundamental and unique structural motif found in pharmaceuticals and natural products. The total syntheses of natural products bearing the benzocycloheptane subunit are challenging and there are only a few efficient approaches to access benzocycloheptane. Thus, new methods and innovative strategies for preparing such natural products need to be developed. In this review, recent progress in the total syntheses of natural products bearing the benzocycloheptane motif is presented, and key transformations for the construction of benzocycloheptane are highlighted. This review provides a useful guide for those engaged in the syntheses of natural products containing the benzocycloheptane motif.

Enantioselective formation of quaternary carbon stereocenters in natural product synthesis: a recent update

Covering: 2013-2018 Natural products bearing quaternary carbon stereocenters have attracted tremendous interest from the synthetic community due to their diverse biological activities and fascinating molecular architectures. However, the construction of these molecules in an enantioselective fashion remains a long-standing challenge because of the lack of efficient asymmetric catalytic methods for installing these motifs. The rapid progress in the development of new-generation efficient chiral catalysts has opened the door for several asymmetric reactions, such as Michael addition, dearomative cyclization, polyene cyclization, α-arylation, cycloaddition, allylation, for the construction of quaternary carbon stereocenters in a highly enantioselective fashion. These asymmetric catalytic methods have greatly facilitated the synthesis of complex natural products with improved output and overall efficiency. In this concise review, we highlight the progress in the last six years in complex natural product synthesis, in which at least one quaternary carbon stereocenter has been constructed via asymmetric catalytic technologies, with particular emphasis on the analysis of the stereochemical model of each enantioselective transformation.

Asymmetric synthesis of 3-benzyl and allyl isoindolinones by Pd-catalyzed dicarbofunctionalization of 1,1-disubstituted enamides

The Pd-catalyzed enantioselective Heck/Suzuki reaction of 1,1-disubstituted enamides with aryl/vinyl boronic acids has been developed to access 3-benzyl/allyl substituted isoindolinones bearing a tetrasubstituted stereogenic carbon center.

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.

Palladium-catalyzed asymmetric dearomative cyclization in natural product synthesis

Asymmetric catalysis is a rapidly growing field in modern organic chemistry and has been indispensable for the synthesis of enantioenriched materials to meet demands from the academies to pharmaceutical industries. Asymmetric dearomative cyclization catalyzed by transition metals has been a hot research area in the last decade. Fascinated by its ability to construct sterically hindered quaternary stereogenic center(s) through dearomatization and simultaneously forging new ring structure(s) through cyclization, palladium-catalyzed asymmetric dearomative cyclization has been applied to the synthesis of structurally complicated natural products and it is increasingly prevalent in the literature. In particular, the resultant product from dearomative cyclization, which usually carries one or more unsaturated C-C bond(s), allows further functional group transformations. Previously reported applications of palladium-catalyzed asymmetric dearomative cyclization in natural product synthesis are presented here and discussed in depth.

Activation of allylic esters in an intramolecular vinylogous kinetic resolution reaction with synergistic magnesium catalysts

Kinetic resolution (KR) of racemic starting materials is a powerful and practical alternative to prepare valuable enantiomerically enriched compounds. A magnesium-catalyzed kinetic resolution based on a designed intramolecular vinylogous Michael reaction is disclosed. Here we show a synergistic catalytic strategy based on the development of chiral ligands. Substrates containing linear allylic ester structures are designed and synthesized to construct key [6.6.5]-tricyclic chiral skeletons via this kinetic resolution process. Detailed mechanistic studies reveal a rational mechanism for the current intramolecular vinylogous KR reaction. The desired direct intramolecular asymmetric vinylogous Michael reaction of linear allylic esters is realized in high efficiency and enantioselectivity with the synergistic catalytic system.

Kinetic resolution allows to obtain enantioenriched compounds from racemic mixtures. Here, the authors report a synergistic magnesium catalyst promoting kinetic resolution of an intramolecular vinylogous Michael reaction to access [6.6.5]-tricyclic chiral skeletons.

Construction of Various Bridged Polycyclic Skeletons by Palladium-Catalyzed Dearomatization

A powerful palladium-catalyzed dearomative cyclization was developed that provides facile access to eight types of bridged tetracyclic skeletons bearing various ring sizes and heterocycles. With this method, several skeletons or analogues of natural products, including tubingensin B and dracaenones, were synthesized. Asymmetric dearomative cyclization enables the construction of various enantiomerically enriched bridged polycyclic systems with up to 99 % ee by employing a chiral palladium catalyst.

Synthesis of the Tetracyclic Framework of Polycyclic Spiro Lignan Natural Products

Polycyclic spiro lignans are a new family of lignan natural products recently isolated from Gymnotheca involucrata. The first synthesis of two model substrates of this rare family of natural products was achieved in six steps. An efficient strategy that features Suzuki coupling and Friedel-Crafts acylation was employed to construct the ABC tricyclic fluorene framework. Subsequently, Grignard reaction followed by acid-mediated cyclization furnished the spiro cyclic ether ring D.

Catalytic asymmetric multiple dearomatizations of phenols enabled by a cascade 1,8-addition and Diels-Alder reaction

A direct catalytic asymmetric multiple dearomatization reaction of phenols was disclosed, which provides expedient access to a series of architecturally complex polycyclic compounds bearing four stereogenic centers in high enantiopurity. The key to achieve such a transformation is the combination of a dearomative 1,8-addition of β-naphthols to para-quinone methides generated in situ from propargylic alcohols and a subsequent intramolecular dearomative Diels–Alder reaction. Noteworthily, this protocol enrichs not only the diversity of dearomatized products but also the toolbox of dearomatization strategies.

The first chiral phosphoric acid catalyzed asymmetric multiple dearomatizations of phenols for the synthesis of bridged polycyclic compounds are reported.

Chiral phosphoric acid catalyzed aminative dearomatization of α-naphthols/Michael addition sequence

Asymmetric dearomatization reactions have recently emerged as a powerful tool for the rapid build-up of the molecular complexity. Chiral three-dimensional polycyclic molecules bearing contiguous stereogenic centers can be synthesized from readily available planar aromatic feedstocks. Here we report that an intermolecular asymmetric dearomatization reaction of α-naphthols bearing a tethered nucleophile at the C4 position of the naphthol ring is achieved by a chiral phosphoric acid. The reaction proceeds via a highly chemo- and regioselective aminative dearomatization/Michael addition sequence, affording a wide array of functionalized cyclic ketones in good yields (up to 93%) with excellent enantioselectivity (up to >99% ee). The catalyst loading can be reduced to 0.1 mol%. Preliminary mechanistic investigations identify that the enantioselectivity is established in the dearomatization step, while the Michael addition is the rate-limiting step. A working model accounting for the origin of the stereochemistry is proposed based on DFT calculations.

Efficient Enantioselective Syntheses of Chiral Natural Products Facilitated by Ligand Design

The employment of enantioselective transition-metal-catalyzed transformations as key steps in asymmetric natural product syntheses have attracted considerable attention in recent years owing to their versatile synthetic utilities, mild conditions and high efficiency in chirality generation. The chiral catalysts or supporting ligands are believed to be crucial for the requisite reactivity and enantioselectivity. Therefore, the rational design of chiral ligands is at the heart of developing new asymmetric transition-metal catalyzed reactions and provides an avenue to the asymmetric synthesis of natural products. Our group has been engaged in the development of transition-metal-catalyzed enantioselective cross-coupling, cyclization and other related reactions and the application of these methodologies to natural product syntheses. In this account, we summarized our recent synthetic efforts towards the efficient total syntheses of several different types of natural products including terpenes, alkaloids and polyketides facilitated by the design of a series of versatile P-chiral phosphorous ligands.

P-Chiral Phosphorus Ligands Based on a 2,3-Dihydrobenzo[ d][1,3]oxaphosphole Motif for Asymmetric Catalysis

Despite the rapid progress in the field of asymmetric catalysis, the search for new, efficient, and practical asymmetric catalytic transformations to facilitate the green synthesis of chiral natural products and drugs will continue to be a major ongoing effort in organic chemistry. Chiral phosphorus ligands have played a significant role in recent advances in transition-metal-catalyzed asymmetric transformations. However, there remain numerous challenging issues of reactivity and selectivity in catalysis. The development of new and efficient chiral phosphorus ligands with new structural motifs remains highly desirable. P-Chiral phosphorus ligands have been overlooked and are underdeveloped, except for the early success of DIPAMP, introduced first by Knowles in the early 1970s. It was not until the late 1990s that the development of P-chiral phosphorus ligands regained attention with the advent of bisP*, TangPhos, etc. Nonetheless, most P-chiral phosphorus ligands were either difficult to prepare or operationally inconvenient. The development of efficient, practical, and operationally convenient P-chiral phosphorus ligands with new structural motifs remains an important subject of research. This Account introduces the design and development of a series of practical and efficient P-chiral bis- and monophosphorus ligands based on a 2,3-dihydrobenzo[ d][1,3]oxaphosphole motif. Their unique structural and physical properties include conformational unambiguousness, high tunability of electronic and steric properties, and operational simplicity as air-stable solids, which make them practical and exceptional ligands for asymmetric catalysis. Chiral bisphosphorus ligands such as MeO-BIBOP (L3), WingPhos (L4), and iPr-BABIBOP (L7) have demonstrated excellent enantioselectivities and unprecedented turnover numbers (TONs) in various asymmetric hydrogenations and other transformations, providing practical and efficient solutions leading to chiral amines, alcohols, carboxylic acids, and α- and β-amino acids. Chiral biaryl monophosphorus ligands, including BI-DIME (L9), AntPhos (L15), iPr-BI-DIME (L11), etc., have proven to be a class of versatile and powerful ligands for a number of catalytic asymmetric transformations, including asymmetric Suzuki-Miyaura coupling, asymmetric palladium-catalyzed dearomative cyclization, asymmetric hydroboration/diboration, asymmetric nickel-catalyzed reductive coupling, asymmetric palladium-catalyzed intramolecular arylation, asymmetric alkene aryloxyarylation, asymmetric α-arylation, asymmetric Heck reaction, and asymmetric nucleophilic addition, providing efficient solutions leading to various synthetically challenging chiral structures such as chiral biaryls, chiral tertiary alcohols, chiral α-amino tertiary boronic esters, and chiral all-carbon quaternary stereocenters. The high enantioselectivities and TONs obtained with these ligands have resulted in the syntheses of several chiral natural products and therapeutic agents in concise and highly efficient manners. While our efforts on the development of P-chiral phosphorus ligands are ongoing, it should be emphasized that the development of ligands and catalysts with new structural motifs should continue in the search for new reactivity and selectivity to tackle current synthetic challenges. Such effort is destined to promote the advances of asymmetric catalysis as well as synthetic organic chemistry.

Synthesis of the core structure of phalarine

Two new palladium-catalyzed reactions enabled the synthesis of the core structure of phalarine.

Total Synthesis of Tetarimycin A, (±)-Naphthacemycin A9, and (±)-Fasamycin A: Structure-Activity Relationship Studies against Drug-Resistant Bacteria

Making use of a reductive olefin coupling reaction and Michael-Dieckmann condensation as two key operations, we have completed a concise total synthesis of tetarimycin A, (±)-naphthacemycin A₉, and (±)-fasamycin A in a highly convergent and practical protocol. Synthetic procedures thus developed have also been applied to provide related analogues for structure-activity relationship studies, thereby coming to the conclusion that the free hydroxyl group at C-10 is essential for exerting inhibitory activities against a panel of Gram-positive bacteria, including drug-resistant strains VRE and MRSA.

Rh-Catalyzed aminative dearomatization of 2-naphthols

β-Naphthalenones bearing a naked α-amino group could be rapidly constructed through a Rh-catalyzed aminative dearomatization reaction of 2-naphthols with O-(2,4-dinitrophenyl)hydroxylamine.

Enantioselective Palladium-Catalyzed Intramolecular α-Arylative Desymmetrization of 1,3-Diketones

An efficient enantioselective protocol has been reported to build highly oxygenated and densely substituted bicyclo[m.n.1] skeletons through intramolecular asymmetric α-arylative desymmetrization of 1,3-diketones. Employing Pd catalyst and FOXAP ligand, various bicyclo[m.n.1] skeleton with different size can be accessed with high enantio- and diastereoselectivities. Utilizing the present method as a key step, formal asymmetric total synthesis of the (-)-parvifoline has been demonstrated.

Total Synthesis of (+)-Gracilamine Based on an Oxidative Phenolic Coupling Reaction and Determination of Its Absolute Configuration

The enantioselective total synthesis of (+)-gracilamine (1) is described. The strategy features a diastereoselective phenolic coupling reaction followed by a regioselective intramolecular aza-Michael reaction to construct the ABCE ring system. The configuration at C3a in 1 was controlled by the stereocenter at C9a, which was selectively generated (91 % ee) by an organocatalytic enantioselective aza-Friedel-Crafts reaction developed by our research group. This synthesis revealed that the absolute configuration of (+)-gracilamine is 3aR, 4S, 5S, 6R, 7aS, 8R, 9aS.