Total Synthesis and Biological Evaluation of the Resveratrol-Derived Polyphenol Natural Products Hopeanol and Hopeahainol A

Asymmetric total syntheses of aspilactonol F and aspiketolactonol and synthetic studies toward diplofuranoxin

The first asymmetric total synthesis of C9 polyketides, aspilactonol F and aspiketolactonol has been achieved. Ring-closing-metathesis has been employed as the key step in the synthesis. The total synthesis of aspilactonol F and aspiketolactonol was accomplished in 8 and 10 steps, in good overall yields of 28% and 24%, respectively, with only four column purifications for the former. A common strategy for the concise synthesis of the key intermediate of diplofuranoxin is also presented.

One-pot domino syntheses of 3-alkyl-3-N-substituted aminobenzofuran-2(3H)-ones based on alkali-promoted Michael addition and lactonization

In this paper, a novel cascade reaction of caesium carbonate-promoted Michael addition and lactonization for the one-pot synthesis of 3-alkyl-3-N-substituted aminobenzofuran-2(3H)-one derivatives has been established based on the screening of the alkaline reagents and optimization of reaction conditions, in which the N-substituted (ortho-hydroxy)aryl glycine esters were used as the Michael donors to react with different α, β-unsaturated carbonyl compounds. In the case of using the asymmetric starting material, the epimers could be successfully separated by conventional chromatography. In addition, plausible mechanisms were suggested and the absolute configuration of the epimer was analysed. All the chemical structures of unreported benzofuran-2(3H)-one derivatives were characterized by 1H nuclear magnetic resonance (NMR), 13C NMR, IR and high-resolution mass spectrometry (HRMS).

Catalyst-Controlled Divergent Generations and Transformations of α-Carbonyl Cations from Alkynes

α-Carbonyl cations are the umpolung forms of the synthetically fundamental α-carbonyl carbanions. They are highly reactive yet rarely studied and utilized species and their precursors were rather limited. Herein, we report the catalyst-controlled divergent generations of α-carbonyl cations from single alkyne functionalities and the interception of them via Wagner-Meerwein rearrangement. Two chemodivergent catalytic systems have been established, leading to two different types of α-carbonyl cations and, eventually, two different types of products, i.e. the α,β- and β,γ-unsaturated carbonyl compounds. Broad spectrum of alkynes including aryl alkyne, ynamide, alkynyl ether, and alkynyl sulfide could be utilized and the migration priorities of different groups in the Wagner-Meerwein rearrangement step was elucidated. Density functional theory calculations further supported the intermediacy of α-carbonyl cations via the N-O bond cleavage in both the two catalytic systems. Another key feature of this methodology was the fragmentation of synthetically inert tert-butyl groups into readily transformable olefin functionalities. The synthetic potential was highlighted by the scale-up reactions and the downstream diversifications including the formal synthesis of nicotlactone B and galbacin.

Direct Two Carbon Ring Expansion of 1-Indanones with Ynones: An Eco-Friendly, One-Flask Approach to Functionally Enriched 5H-Benzo[7]annulenes

Direct 2C-ring expansion of 1-indanones with ynones to 5H-benzo[7]annulenes has been observed, and its generality has been gauged (19 examples). Overall, this simple and convenient cascade process to 5H-benzo[7]annulenes involves engagement of 1-indanone with two ynone moieties with formation of three new C-C σ-bonds, cleavage of C-C σ-bond, and concurrent functionality amplification. The resulting seven-membered ring, laced with an opportunistic disposition of four proximal functional groups, offers avenues for their further productive interplay. Our new approach embraces many green and eco-friendly features.

Visible-Light-Induced Desaturative β-Alkoxyoxalylation of N-Aryl Cyclic Amines with Difluoromethyl Bromides and H2O Via a Triple Cleavage Process

A visible-light-driven desaturative β-alkoxyoxalyation of N-aryl cyclic amines with difluoromethyl bromides and H2O has been reported. This tandem reaction is triggered by homolysis of the C-Br bond to produce the difuoroalkyl radical, which undergoes the subsequent defluorinated β-alkoxyoxalylation cascades to afford a wide range of β-ketoester/ketoamides substituted enamines. The prominent feature of this reaction contains photocatalyst-free, transition-metal free, and mild conditions. The 18O labeling experiment disclosed that H2O is the oxygen source of the carbonyl unit.

A Diastereoselective Assembly of Tetralone Derivatives via a Tandem Michael Reaction and ipso-Substitution of the Nitro Group

A highly diastereoselective tandem reaction of 2'-nitrochalcones is reported, involving Michael addition and a subsequent ipso-substitution of the nitro group to produce 1-tetralones with two contiguous chiral centers. A related annulation reaction of 2'-nitrochalcones with potassium cyanide affording 1-indanones with a C3-quaternary chiral center is also demonstrated.

Enantioselective Synthesis of Spiro Heterocyclic Compounds Using a Combination of Organocatalysis and Transition-Metal Catalysis

Over the last ten years, the combination of organocatalysis with transition metal (TM) catalysis has become one of the most important toolboxes used for synthesizing optically pure compounds containing chiral quaternary centers, including spiro heterocyclic molecules. The dominant method in the enantioselective synthesis of spiro heterocyclic compounds based on synergistic catalysis includes chiral aminocatalysis and NHC catalysis, as already established covalent organocatalytic strategies. Another area of organocatalysis widely combined with TM catalysis producing enantiomerically enriched spiro heterocyclic compounds is non-covalent catalysis, dominated by chiral phosphoric acids, thiourea, and squaramide derivatives. This review article aims to summarize enantioselective methods used for constructing spirocyclic heterocycles based on a combination of organocatalysis and transition metal catalysis.

Synthesis, Biosynthesis, and Biological Activity of Diels-Alder Adducts from Morus Genus: An Update

The plants of the Moraceae family are producers of a great variety of polyphenolic natural products. Among these, the Diels-Alder type adducts (DAAs) are endowed with a unique cyclohexene scaffold, since they are biosynthesized from [4+2] cycloaddition of different polyphenolic precursors such as chalcones and dehydroprenyl polyphenols. To date, more than 150 DAAs have been isolated and characterized from Moraceous and related plants. The main source of DAAs is the mulberry root bark, also known as "Sang-Bai-Pi" in Traditional Chinese Medicine, but they have also been isolated from root bark, stem barks, roots, stems or twigs, leaves, and callus cultures of Moraceous and other related plants. Since 1980, many biological activities of DAAs have been identified, including anti-HIV, antimicrobial, anti-inflammatory, and anticancer ones. For these reasons, natural DAAs have been intensively investigated, and a lot of efforts have been made to study their biosynthesis and to establish practical synthetic access. In this review, we summarized all the updated knowledge on biosynthesis, chemoenzymatic synthesis, racemic and enantioselective total synthesis, and biological activity of natural DAAs from Moraceous and related plants.

Computation-Guided Total Synthesis of Vitisinol G

Computational chemistry is useful in synthetic organic chemistry, as it can be used not only to analyze reaction mechanisms, but also to calculate biosynthetic pathways and to plan and evaluate strategies for total syntheses. Here we report the computation-guided total synthesis of vitisinol G, a resveratrol dimer.

Vicinal ketoesters – key intermediates in the total synthesis of natural products

This review summarizes examples for the application of vicinal ketoesters such as α-ketoesters, mesoxalic esters, and α,β-diketoesters as key intermediates in the total synthesis of natural products utilizing their electrophilic keto group as reactive site. Suitable key reactions are, e.g., aldol additions, carbonyl ene reactions, Mannich reactions, and additions of organometallic reagents. The vicinal arrangement of carbonyl groups allows the stabilization of reactive conformations by chelation or dipole control.

Cu(I)-Catalyzed C-H Alkenylation of Tertiary C(sp3)-H Bonds of 3-Aryl Benzofuran-2(3H)-ones to Give Z- and E-Styrene Containing Quaternary Carbon Centers with 99/1 Regioselectivity

The synthesis of isomerically pure olefins containing all-carbon quaternary centers is a challenging issue. Herein, we developed an efficient protocol for the synthesis of (Z)-olefins (27 examples, yield up to 97%, Z/E up to 99/1) and (E)-olefins (16 examples, yield up to 94%, E/Z up to 99/1) containing all-carbon quaternary centers. This protocol is adopted for the copper-catalyzed regioselective C-H alkenylation of the tertiary C(sp³)-H bond of 3-aryl benzofuran-2(3H)-ones with alkyne and alkenes. A diverse range of functional groups in the substrates is well-tolerated, such as F, Cl, Br, Me, OMe, ester, CF₃, etc. A gram scale experiment was performed in good yield, and the radical mechanisms are also proposed based on the control experiments.

Enantioselective construction of spiro-tetrahydroquinoline scaffolds through asymmetric catalytic cascade reactions

An efficient and concise strategy has been successfully developed for merging spiro-tetrahydroquinoline with spiro-benzofuranone into a single new skeleton through asymmetric catalytic cascade reactions catalyzed by quinine-derived chiral bifunctional squaramide organocatalysts. In this approach, differently substituted spiro-tetrahydroquinoline derivatives were smoothly obtained with high yields, and excellent diastereoselectivities and enantioselectivities (up to 99% yield, up to >20 : 1 dr, up to >99% ee, 40 examples) under mild reaction conditions.

Destabilized Carbocations Caged in Water Microdroplets: Isolation and Real-Time Detection of α-Carbonyl Cation Intermediates

Over the last 50 years, proposals of α-carbonyl cation intermediates have been driven by chemical intuition and indirect evidence. Recently, wide interest in α-carbonyl cation chemistry has opened new gates to prepare α-functionalized carbonyl compounds. Though these intrinsically unstable carbocations are formed under forcing conditions (e.g., in a strong acid medium), their fleeting existence prohibits direct observation or spectroscopic measurement. We report that high-speed aqueous microdroplets can directly capture α-carbonyl cation intermediates from various reactions (Friedel-Crafts arylation, deoxygenation, and azidation) upon bombarding with the corresponding reaction aliquots. The α-carbonyl cations caged in water droplets are then desorbed to the gas phase, allowing their successful measurement by mass spectrometry. This has also enabled us to simultaneously monitor the relative abundance of the associated precursor, α-carbonyl cation intermediate, and product during the progress of the reaction.

Computation-guided asymmetric total syntheses of resveratrol dimers

Although computational simulation-based natural product syntheses are in their initial stages of development, this concept can potentially become an indispensable resource in the field of organic synthesis. Herein we report the asymmetric total syntheses of several resveratrol dimers based on a comprehensive computational simulation of their biosynthetic pathways. Density functional theory (DFT) calculations suggested inconsistencies in the biosynthesis of vaticahainol A and B that predicted the requirement of structural corrections of these natural products. According to the computational predictions, total syntheses were examined and the correct structures of vaticahainol A and B were confirmed. The established synthetic route was applied to the asymmetric total synthesis of (−)-malibatol A, (−)-vaticahainol B, (+)-vaticahainol A, (+)-vaticahainol C, and (−)-albiraminol B, which provided new insight into the biosynthetic pathway of resveratrol dimers. This study demonstrated that computation-guided organic synthesis can be a powerful strategy to advance the chemical research of natural products.

Although computational simulation-based natural product syntheses are in their initial stages of development, this concept can potentially become an indispensable resource in the field of organic synthesis. Here the authors report asymmetric total syntheses of several resveratrol dimers based on a comprehensive computational simulation of their biosynthetic pathways.

Diastereoselective synthesis of chroman bearing spirobenzofuranone scaffolds via oxa-Michael/1,6-conjugated addition of para-quinone methides with benzofuranone-type olefins

A simple and convenient cyclization of ortho-hydroxyphenyl-substituted para-quinone methides with benzofuran-2-one type active olefins via oxa-Michael/1,6-conjugated addition has been developed, which afforded an easy access to enriched functionalized chroman-spirobenzofuran-2-one scaffolds with good to excellent yields (up to 90%) and diastereoselectivities (up to >19 : 1 dr). This reaction provided an efficient method for constructing desired spirocyclic compounds combining both well-known heterocyclic pharmacophores chroman and benzofuran-2-one.

Highly diastereoselective synthesis of spirocyclic compounds combining both well-known heterocyclic pharmacophores chroman and benzofuran-2-one.

Recent Advances on Benzofuranones: Synthesis and Transformation via C–H Functionalization

The benzofuranone structure is important in many fields, such as natural products, pharmaceuticals, building blocks, antioxidants, and dyes. The efficient synthesis and transformation of benzofuranones have attracted great attention in organic synthesis. They can be synthesized by the Friedel–Crafts reaction and intramolecular dehydration ring-closing and transition-metal-catalyzed reactions, among others. Their direct utilization in the preparation of other functional molecules further enhance their application. Due to their low pK a value and easy enolization, the transformation of benzofuranones via C(3)–H bond functionalization has been a hot issue since 2010. Herein, we highlight advances in the synthesis of benzofuranones and their transformation via C–H functionalization. Other transformations related to benzofuranones are also discussed.

1 Introduction

2 Synthesis of Benzofuranones

3 C–H Functionalization of Benzofuranones

4 Other Types of Reactions of Benzofuranones

5 Conclusion and Outlook

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.

Cu-Catalyzed radical-triggered spirotricyclization of enediynes and enyne-nitriles for the synthesis of pentacyclic spiroindenes

A new copper-catalyzed radical-triggered fluoromethylation-spirotricyclization of enediyne- and enyne-nitrile-containing para-quinone methides (p-QMs) was reported for the first time, and used to produce a series of hitherto unreported pentacyclic spiroindenes.

TfOH-Catalyzed Cascade C-H Activation/Lactonization of Phenols with α-Aryl-α-diazoesters: Rapid Access to α-Aryl Benzofuranones

Aryl benzofuranones are privileged structural units present in natural products and pharmaceutically relevant compounds with high bioactivity and therapeutic value; synthetic access to these scaffolds remains an area of intensive interest. A new and efficient TfOH-catalyzed cascade ortho C-H activation/lactonization of phenols with α-aryl-α-diazoacetates is reported. This metal-free protocol provides an operationally simple and rapid method for the one-pot assembly of diverse α-aryl benzofuranones in high yields with broad substrate scope, a readily starting material, good chemo-regioselectivity, and excellent functional group compatibility.

Metal-Catalyzed Spiroannulation-Fluoromethylfunctionaliztions of 1,5-Enynes for the Synthesis of Stereodefined (Z)-Spiroindenes

Two classes of new catalytic spiroannulation-fluormethylfunctionaliztions of para-quinone methide (p-QM)-containing 1,5-enynes have been established under redox-neutral conditions. Palladium-catalyzed spiroannulation-iododifluoromethylation with ethyl difluoroiodoacetate oriented completely stereoselective access to (Z)-spiroindenes and the latter included copper-catalyzed three-component spiroannulation-cyanotrifluoromethylation starting from Togni's reagent and trimethylsilanecarbonitrile (TMSCN). Both reaction pathways involve fluoroalkyl radical-triggered 1,6-addition/5-exo-dig annulation/metal radical cross-coupling/reductive elimination sequence, providing practical and stereoselective protocols for rapidly constructing cyclohexadienone-containing spiroindenes with generally good yields.

Synthesis of Vitisins A and D Enabled by a Persistent Radical Equilibrium

The first total synthesis of the resveratrol tetramers vitisin A and vitisin D is reported. Electrochemical generation and selective dimerization of persistent radicals is followed by thermal isomerization of the symmetric C8b-C8c dimer to the C3c-C8b isomer, providing rapid entry into the vitisin core. Computational results suggest that this synthetic approach mimics Nature's strategy for constructing these complex molecules. Sequential acid-mediated rearrangements consistent with the proposed biogenesis of these compounds afford vitisin A and vitisin D. The rapid synthesis of these complex molecules will enable further study of their pharmacological potential.

Resveratrol: a review of plant sources, synthesis, stability, modification and food application

Resveratrol, a stilbene molecule belonging to the polyphenol family, is usually extracted from a great many natural plants. The technologies of preparation and extraction methods are developing rapidly. As resveratrol has many beneficial properties, it has been widely utilized in food and medicine industry. In terms of its structure, it is susceptible to degradation and can undergo chemical changes during food processing. Different studies have therefore given more attention to various aspects of resveratrol, including anti-aging, anti-oxidant, and anti-cancer activity. This review classifies the study of resveratrol, considers plant sources, synthesis, stability, common reactions, and food applications, and provides references to boost its food and medical utilization. © 2019 Society of Chemical Industry.

Bridging free radical chemistry with drug discovery: A promising way for finding novel drugs efficiently

Many diseases have been regarded to correlate with the in vivo oxidative damages, which are caused by overproduced free radicals from metabolic process or reactive oxygen species (ROS). This background motivates chemists to explore free radical reactions and to design a number of antioxidants, but whether free radical chemistry can be applied to accelerate the efficacy of the drug discovery is still underrepresented. Herein, in light of recent findings as well as kinetics on free radical reaction, the discipline of free radical chemistry is introduced to be a novel tool for finding potential drugs from antioxidant libraries accumulated during the study on free radical chemistry. These antioxidants provide with such abundant types of structural skeleton that might be employed to inhibit oxidations in different biological microenvironments. Although the in vitro characterization on the antioxidative property exerts a potential role of an antioxidant as a prodrug, the in vivo investigation on the property for quenching free radicals will make a final decision for the antioxidant whether it is worthy to be further explored pharmacologically. Therefore, it is reasonable to expect that bridging free radical chemistry with the pharmacological research will provide with a succinct way for finding novel drugs efficiently.

Rhodium(iii)-catalysed cascade [3 + 2] annulation of N-aryloxyacetamides with 3-(hetero)arylpropiolic acids: synthesis of benzofuran-2(3H)-ones

Herein, a cascade [3 + 2] annulation of N-aryloxyacetamides with 3-(hetero)arylpropiolic acids affording benzofuran-2(3H)-ones via rhodium(iii)-catalyzed redox-neutral C-H functionalization/isomerization/lactonization using an internal oxidative directing group O-NHAc was achieved. This catalytic system provides a regio- and stereoselective approach to synthesize (Z)-3-(amino(aryl)methylene)benzofuran-2(3H)-ones with exclusive Z configuration selectivity, acceptable yields and good functional group tolerance. Preliminary investigations on ultraviolet-visible and fluorescence behaviors reveal that the annulation products may be applied as a promising fluorescent probe for sensing metal cations, especially for cerium (Ce3+).

C(sp3)-H hydroxylation of fluorenes, oxindoles and benzofuranones with a Mg(NO3)2-HP(O)Ph2 oxidation system

A novel oxidation system in which magnesium nitrate [Mg(NO₃)₂] is used as an oxidant in the presence of diphe-nylphosphine oxide [HP(O)Ph₂] permits the C(sp³)-H hydroxylation of fluorenes, oxindoles, and benzofuranones. This method features high efficiency, good functional group tolerance, and operational simplicity. The synthetic utility is highlighted by further transformations to valuable organic materials.

A bifunctional pyrazolone–chromone synthon directed organocatalytic double Michael cascade reaction: forging five stereocenters in structurally diverse hexahydroxanthones

The merging of two or more known natural product-based scaffolds is a powerful and routine strategy to develop bioactive small molecules.

Stereocontrolled construction of six vicinal stereogenic centers on a hexahydroxanthone framework through a formal [2+1+3] annulation

The first example of a bifunctional donor–donor 3C synthon formed in situ from an activated methine with nitromethane through a [2+1] Michael addition, further directing a one-pot organocascade Michael/Henry cycloaddition was developed.

3-Hydroxy-3-((3-methyl-4-nitroisoxazol-5-yl)methyl)indolin-2-one as a versatile intermediate for retro-Henry and Friedel–Crafts alkylation reactions in aqueous medium

The first example of a retro-Henry type reaction is reported using 3-hydroxy-3-((3-methyl-4-nitroisoxazol-5-yl)methyl)indolin-2-ones which are prepared via catalyst-free Henry reaction of 3,5-dimethyl-4-nitroisoxazole and isatin.

Applications of Friedel-Crafts reactions in total synthesis of natural products

Over the years, Friedel-Crafts (FC) reactions have been acknowledged as the most useful and powerful synthetic tools for the construction of a special kind of carbon-carbon bond involving an aromatic moiety. Its stoichiometric and, more recently, its catalytic procedures have extensively been studied. This reaction in recent years has frequently been used as a key step (steps) in the total synthesis of natural products and targeted complex bioactive molecules. In this review, we try to underscore the applications of intermolecular and intramolecular FC reactions in the total syntheses of natural products and complex molecules, exhibiting diverse biological properties.

Recent applications of the 1,2-carbon atom migration strategy in complex natural product total synthesis

1,2-Carbon atom rearrangement has been broadly applied as a guiding strategy in complex molecule assembly. As it entails the carbon-carbon or carbon-heteroatom bond migration between two vicinal atoms, this type of reaction is capable of generating structural complexity through a molecular skeletal reorganization. This review will focus on recent employment of this strategy in the total synthesis of natural products, highlighting the exceptional utility of such synthetic methodologies in the construction of intricate carbocycles, heterocycles or structurally complex motifs from synthetically more accessible precursors.

Synthesis of Indole-, Benzo[ b]thiophene-, and Benzo[ b]selenophene-Based Analogues of the Resveratrol Dimers Viniferifuran and (±)-Dehydroampelopsin B

A convenient synthetic strategy to obtain viniferifuran and (±)-dehydroampelopsin B analogues based on the heterocyclic cores of indole, benzo[ b]thiophene, and benzo[ b]selenophene is presented. The key transformations utilized in the described syntheses include Sonogashira couplings, Cacchi and alkyne electrophilic cyclizations, Horner-Wadsworth-Emmons (HWE) reaction, chemoselective Suzuki-Miyaura couplings, and acid-promoted intramolecular cyclization to form the seven-membered ring of (±)-dehydroampelopsin B.

Lewis acid-catalyzed Friedel–Crafts reactions toward highly versatile, α-quaternary oxime ethers

Tertiary 2-hydroxy oxime ethers are converted into α-functionalized, all-carbon-substituted products under Lewis acid catalysis in a S_N1-reaction.

α-Carbonyl Cations in Sulfoxide-Driven Oxidative Cyclizations

The selective, metal-free generation of α-carbonyl cations from simple internal alkynes was accomplished by the addition of a sulfoxide to a densely substituted vinyl cation. The high reactivity of the α-carbonyl cations was found to efficiently induce hydrogen and even carbon shift reactions with unusual selecivities. Complex compounds with highly congested tertiary and all-carbon-substituted quartenary carbon centers can thus be accessed in a single step from simple precursors. Mechanistic analysis strongly supports the intermediacy of the title compounds and provides a simple predictive scheme for the migratory aptitude of different substituents.

An enantioselective conjugate addition reaction of 3-substituted benzothiophen-2-ones and 2-phthalimidoacrylates

A highly enantioselective conjugate addition reaction of 3-substituted benzothiophen-2-ones to 2-phthalimidoacrylates has been developed using a bifunctional tertiary-amine thiourea catalyst.

Mechanistic investigation on radical-induced construction of oxindoles: radical versus electrophilic cyclization

A four-step mechanism is established for the title reaction and the radical cyclization is updated to the cationic cyclization.

Total Synthesis of Viniferifuran, Resveratrol-Piceatannol Hybrid, Anigopreissin A and Analogues - Investigation of Demethylation Strategies

Resveratrol-based natural products constitute a valuable source of unique compounds with diverse biological activities. In this report we investigate demethylation strategies to minimize formation of cyclized and dimerized products during the synthesis of viniferifuran and analogues. We found that boron trichloride/tetra-n-butylammonium iodide (BCl3/TBAI) is typically more effective than boron tribromide (BBr3). Based on these findings we carried out the first syntheses of dehydro-δ-viniferin, resveratrol-piceatannol hybrid and anigopreissin A. In addition, we have developed a short and efficient route to viniferifuran that was obtained in 13% yield over six steps.

Total Synthesis of (±)-Kuwanol E

The total synthesis of the Diels-Alder-type adducts (±)-kuwanol E and the heptamethyl ether derivative of (±)-kuwanon Y has been accomplished via a convergent strategy involving 2'-hydroxychalcone 6 or 9 and dehydroprenylstilbene 7, in nine steps. The synthesis features, as a key step, a Lewis acid-mediated biomimetic intermolecular Diels-Alder [4+2] cycloaddition for the construction of the cyclohexene skeleton with three stereogenic centers. Notably, the endo/exo diastereoselectivity of the reaction proved to be temperature-controlled.