A thermal dehydrogenative Diels-Alder reaction of styrenes for the concise synthesis of functionalized naphthalenes

Domino Three-Component N-Acylation/[4 + 2] Cycloaddition/Alder-ene Synthesis of Polysubstituted Benzo[f]isoindole-4-carboxylic Acids

Diversely substituted, partially saturated benzo[f]isoindole-4-carboxylic acids were synthesized by a new three-component reaction (3CR) starting from cinnamic amines (3-arylallylamines), maleimides, and maleic anhydride. The process consists of N-acylation of the amines by maleic anhydride, intramolecular [4 + 2] cycloaddition in vinylarenes (the IMDAV reaction), and the concluding Alder-ene reaction between Diels-Alder intermediates and maleimides. All of the reaction steps proceed in a highly regio- and stereoselective manner, furnishing five adjacent chiral centers and leading to a single diastereoisomer of the title compound. The efficiency of the transformation is secured by thermal conditions or utilization of soft Lewis acids (Yb(OTf)3) as catalysts. The kinetics and mechanism of the 3CR were studied by using dynamic 19F NMR. Based on the NMR data and density functional theory (DFT) calculations, the IMDAV, not the Alder-ene, reaction is the rate-limiting step of the entire process.

Hydrogen-Atom-Transfer-Initiated Radical/Polar Crossover Annulation Cascade for Expedient Access to Complex Tetralins

A radical/polar crossover annulation between allyl-substituted arenes and electron-deficient alkenes is described. Cobalt-catalyzed hydrogen atom transfer (HAT) facilitates tandem radical C-C bond formation that generates functionalized tetralin products in the face of potentially problematic hydrofluorination, hydroalkoxylation, hydrogenation, alkene isomerization, and radical polymerization reactions. The reactions proceed under mild conditions that tolerate many functional groups, leading to a broad substrate scope. This powerful ring-forming reaction very quickly assembles complex tetralins that are the formal products of the largely infeasible Diels-Alder cycloadditions of styrenes.

Photocatalytic Cascade Cyclization of Aryl Haloalkynyl Ketones Forming Cyclopenta[b]naphthalene Derivatives

An efficient metal-free, photoredox-mediated cascade cyclization of aryl 1-haloalk-5-ynyl ketones has been developed. Using catalytic amounts of eosin Y (EY) and EtNMe₂ as a reductive quencher, various aryl 1-haloalk-5-ynyl ketones have been transformed into the corresponding cyclization products in up to 98% yield. As a result, synthetic access to differently α-functionalized cyclopenta[b]naphthones and direct construction of cyclopenta[b]naphtholes has been developed.

Intramolecular Diels-Alder Reactions of α-Bromostyrene-Functionalized Unsaturated Carboxamides

Intramolecular cycloaddition reactions of α-bromostyrene-functionalized amides of monomethyl fumarate were investigated. The reaction of the amides with Et₃N in toluene at 110 °C gave 1,4-dihydronaphthalenes. The 1,4-dihydronaphthalenes may be produced via the intramolecular Diels-Alder reaction, proton transfer, and dehydrobromination by a base, along with C═C bond isomerization by proton transfer. The reaction of amide derivatives with halogen on a benzene ring and alkali metal carbonates in toluene at 110 °C gave naphthalene derivatives directly. Dehydrogenation of various 1,4-dihydronaphthalenes with cesium or rubidium carbonate in toluene at 110 °C gave naphthalene derivatives. The retardation by TEMPO, acceleration by air for some substrates, and density functional theory calculations suggest a radical mechanism caused by intervention of molecular oxygen.

A Removable Acyl Group Promoted the Intramolecular Dehydro-Diels-Alder Reaction of Styrene-Ynes: Highly Chemoselective Synthesis of Aryldihydronaphthalene Derivatives

A removable acyl group promoted the intramolecular didehydro-Diels-Alder reaction of styrene-ynes under mild reaction conditions is proposed. The reaction is free of metals and catalysts, is easy to perform, and exhibits good functional group tolerance, providing a highly chemoselective approach for obtaining the valuable aryldihydronaphthalene derivatives.

IntraMolecular Diels–Alder Reactions of Vinylarenes and Alkynyl Arenes (the IMDAV Reaction)

This comprehensive review summarizes the published literature data concerning the intramolecular Diels–Alder reactions of vinylarenes (the IMDAV reaction) and alkynyl arenes from 1970 to 2019, and covers mainly intramolecular [4+2] cycloaddition reactions of vinyl- or acetylene-substituted furans, thiophenes, pyrroles, indoles, imidazoles, benzenes, and naphthalenes, in which the unsaturated substituent is linked directly to an arene moiety. The selected area of the Diels–Alder reaction differs from other forms of [4+2] cycloadditions due to the uniqueness of the diene fragment, which, along with an exocyclic multiple bond, includes the double bond of an aromatic or heteroaromatic nucleus in its system. Thus, during the formation of the [4+2] cycloaddition intermediate, the aromaticity of furan, thiophene and even benzene rings is broken, leading, as a rule, to the formation of heterocyclic structures rarely accessible by other methods, in contrast to the majority of intermolecular Diels–Alder reactions, with the highest degree of chemo-, regio-, and diastereoselectivity. Therefore, the IMDAV approach is often used for the synthesis of naturally occurring and bioactive molecules, which are also discussed in this review alongside other applications of this reaction. Whenever possible, we have tried to avoid examples of radical, photochemical, oxidative, precious-metal-complex-catalyzed cyclizations and other types of formal [4+2] cycloadditions, focusing on thermal Diels–Alder reactions in the first step, according to the classical mechanism. The second stage of the process, aromatization, is unique for many initial substrates, and hence considerable attention in this overview is given to the detailed description of the reaction mechanisms.

1 Introduction

2 IMDAV Reactions of Vinylfurans

2.1 Alkenes as Internal Dienophiles

2.2 Alkynes and Allenes as Internal Dienophiles

3 IMDAV Reactions of Vinylthiophenes

3.1 Alkenes as Internal Dienophiles

3.2 Alkynes as Internal Dienophiles

4 IMDAV Reactions of Vinylbenzothiophenes

5 IMDAV Reactions of Vinylpyrroles

6 IMDAV Reactions of Vinylindoles

6.1 Alkenes as Internal Dienophiles

6.2 Alkynes as Internal Dienophiles

7 IMDAV Reactions of Styrenes and Vinylnaphthalenes

7.1 Alkenes as Internal Dienophiles

7.2 Alkynes as Internal Dienophiles

7.3 Alkynes as Internal Dienophiles in Aryl Acetylenes (the Intramolecular Dehydro Diels–Alder Reaction)

8 IMDAV Reactions of Vinylimidazoles, Vinylisoxazoles and Vinylpyridines

9 Conclusion

10 Abbreviations

Facile synthesis of diverse hetero polyaromatic hydrocarbons (PAHs) via the styryl Diels–Alder reaction of conjugated diynes

The intramolecular styryl Diels–Alder reaction with conjugated diynes under thermally stable triazole-gold (TA–Au) catalytic conditions and the sequential transformation through alkyne activation to access various PAHs with high efficiency was reported for the first time.

Practical access to fluorescent 2,3-naphthalimide derivatives via didehydro-Diels-Alder reaction

A practical and efficient approach for the synthesis of fluorescent 2,3-naphthalimide derivatives has been developed from readily available starting materials via an intramolecular didehydro-Diels-Alder reaction, which proceeded well under room temperature, exhibiting a wide substrate scope and good functional group tolerance. The practicability of this methodology has been verified by one-step synthesis of the environmentally sensitive fluorophore 6-DMN on a gram scale with a shorter time, fewer steps and less waste disposal, and without the utilization of toxic transition metals. The present experimental and computational studies support the crucial role of the propiolimide moiety in the transformation.

Synthesis of fused 1,2-naphthoquinones with cytotoxic activity using a one-pot three-step reaction

A method for the synthesis of fused 1,2-naphthoquinones, as analogues of biologically active natural terpene quinones, is described. The intermediate polycyclic naphthalenes were prepared by a one-pot palladium-catalysed process from simple alkynes, one of which was made from an optically pure biomass-derived levoglucosenone. The prepared methoxy-substituted naphthalenes were subsequently transformed in one step to 1,2-naphthoquinones by a trivalent-iodine-mediated oxidation. The naphthoquinone products were found to have cytotoxic properties.

Synthesis of Illudinine from Dimedone and Identification of Activity as a Monoamine Oxidase Inhibitor

The fungal metabolite illudinine is prepared in seven steps and ca. 55% overall yield from dimedone using an "open and shut" (ring-opening and ring-closing) strategy. Tandem ring-opening fragmentation and olefination of dimedone establishes alkyne and vinylarene functionality linked by a neopentylene tether. Oxidative cycloisomerization then provides the illudinine framework. The key innovation in this second-generation synthesis of illudinine is the use of the nitrile functional group, rather than an ester, as the functional precursor to the carboxylic acid of illudinine. The small, linear nitrile (C≡N) is associated with improved selectivity, π-conjugation, and reactivity at multiple points in the synthetic sequence relative to the carboxylic acid ester. Preliminary assays indicate that illudinine and several related synthetic analogues are monoamine oxidase inhibitors, which is the first reported indication of biological activity associated with this natural product. Illudinine was found to inhibit monoamine oxidase B (MAO-B) with an IC₅₀ of 18 ± 7.1 μM in preliminary assays.

Cu(I)-Catalyzed addition-cycloisomerization difunctionalization reaction of 1,3-enyne-alkylidenecyclopropanes (ACPs)

A copper(i)-catalyzed three-component addition-cycloisomerization difunctionalization reaction of 1,3-enyne-ACPs with Togni I reagent and TMSCN under mild reaction conditions has been developed, affording 3-trifluoroethylcyclopenta[b]naphthalene-4-carbonitrile derivatives. The reaction proceeded through a copper(i)-catalyzed 1,4-addition of conjugated 1,3-enynes via a radical relay process and aromatic cycloisomerization of allene-ACP intermediates.

BF3-Catalyzed Skeletal Rearrangement of 7-En-2-ynones to endo-Type Cyclic Dienes

Transition-metal-catalyzed cycloisomerization reactions with skeletal rearrangement of 1,n-enynes to afford cyclic dienes (particularly exo-cyclization products) have been well studied. However, there are few reports on the nonmetal-catalyzed skeletal rearrangement of enynes and skeletal rearrangement of electron-deficient enynes such as n-en-2-ynones. Here, we describe BF₃·MeCN-catalyzed synthesis of 3-alkylidenecyclohexenes from 7-en-2-ynones, representing the first nonmetal-catalyzed skeletal rearrangement of 1,6-enynes to endo-type cyclic dienes.

Microwave Heating Outperforms Conventional Heating for a Thermal Reaction that Produces a Thermally Labile Product: Observations Consistent with Selective Microwave Heating

Microwave (MW) heating is more effective than conventional (CONV) heating for promoting a high-temperature oxidative cycloisomerization reaction that was previously reported as a key step in a total synthesis of the natural product illudinine. The thermal reaction pathway as envisioned is an inverse electron-demand dehydro-Diels-Alder reaction with in situ oxidation to generate a substituted isoquinoline, which itself is unstable to the reaction conditions. Observed reaction yields were higher at a measured bulk temperature of 200 °C than at 180 °C or 220 °C; at 24 hours than at earlier or later time points; and when the reaction solution was heated using MW energy as opposed to CONV heating with a metal heat block. Selective MW heating of polar solute aggregates is postulated to explain these observations.

Intramolecular Diels-Alder Reaction of a Silyl-Substituted Vinylimidazole en Route to the Fully Substituted Cyclopentane Core of Oroidin Dimers

An intramolecular Diels-Alder reaction of a silyl-substituted vinylimidazole delivers a diastereomeric mixture of C4-silyl functionalized dihydrobenzimidazoles. Subsequent diastereoselective reduction and elaboration of the lactone gives rise to a polysubstituted tetrahydrobenzimidazole, which, upon oxidative rearrangement, affords a single spirofused imidazolone containing all of the relevant functionality for an approach to the oroidin dimers axinellamine, massadine, and palau'amine.

Stereoselective Synthesis of Highly Substituted Tetrahydropyrans through an Evans Aldol-Prins Strategy

A direct and general method for the synthesis of naturally occurring 2,3,4,5,6-pentasubstituted tetrahydropyrans has been developed, employing β,γ-unsaturated N-acyl oxazolidin-2-ones as key starting materials. The combination of the Evans aldol addition and the Prins cyclization allowed the diastereoselective and efficient generation of the desired oxacycles in two fashions: a one-pot Evans aldol-Prins protocol, in which five new σ bonds and five contiguous stereocenters were straightforwardly generated, and a two-step version, which additionally permitted the isolation of β,γ-unsaturated alcohol precursors bearing an N-acyl oxazolidin-2-one in the α position. From these alcohols were also obtained halogenated pentasubstituted tetrahydropyrans as well as 2,3,4,5-tetrasubstituted tetrahydrofurans, shedding light on the mechanism of the process. Computational studies were consistent with the experimental findings, and this innovative Evans aldol-Prins strategy was performed for the preparation of a battery of more than 30 densely substituted tetrahydropyrans, unprecedentedly fused to a 1,3-oxazinane-2,4-dione ring, both in a racemic fashion and in an enantiomeric fashion. These novel molecules were successfully submitted to several transformations to permit simple access to a variety of differently functionalized tetrahydropyrans. Most of these unique molecules were evaluated for their antimicrobial activity against Gram-positive and Gram-negative bacteria and the yeast Candida albicans, and some structure-activity relationships were established.

Base-Promoted Selective Synthesis of 2H-Pyranones and Tetrahydronaphthalenes via Domino Reactions

A highly efficient domino protocol has been developed for the synthesis of 6-aryl-4-(methylthio/amine-1-yl)-2-oxo-2H-pyran-3-carbonitriles and 4-aryl-2-(amine-1-yl)-5,6,7,8-tetrahydronaphthalene-1-carbonitriles from simple and readily available α-aroylketene dithioacetals, malononitrile, secondary amines, and cyclohexanone. This elegant domino process involved consecutive addition-elimination, intramolecular cyclization, and ring opening and closing sequences. Notably, in situ generated 2-imino-4-(methylthio/amine-1-yl)-6-aryl-2H-pyran-3-carbonitrile plays multiple roles in the construction of various novel polyaromatic hydrocarbons.

Synthesis of Illudinine from Dimedone

A total synthesis of the illudalane sesquiterpene illudinine was realized in eight steps and 14% overall yield from commercially available dimedone. The approach features tandem fragmentation/Knoevenagel-type condensation and microwave-assisted oxidative cycloisomerization to establish the isoquinoline core. Completion of the synthesis involves a recently reported cascade S_NAr/Lossen rearrangement on a densely functionalized aryl bromide and an optimized procedure for O-methylation of 8-hydroxyisoquinolines. The oxidative cycloisomerization proceeds by way of a novel inverse-demand intramolecular dehydro-Diels-Alder cycloaddition, which has a potentially broader appeal for preparing substituted isoquinolines.

Synthesis and photophysical studies of through-space conjugated [2.2]paracyclophane-based naphthalene fluorophores

New three-dimensional compact organic fluorophores with tunable photophysical properties are easily accessible from [2.2]paracyclophane using an intramolecular dehydrogenative Diels–Alder reaction as a key step.

An atom- and pot-economical consecutive multi-step reaction approach to polycyclic aromatic hydrocarbons (PAHs)

A novel [4+2]-benzannulation approach to substituted polycyclic aromatic hydrocarbons has been developed under atom-economical, mild and metal-free reaction conditions.

Intramolecular [2 + 2] and [4 + 2] Cycloaddition Reactions of Cinnamylamides of Ethenetricarboxylate in Sequential Processes

Intramolecular [2 + 2] and [4 + 2] cycloaddition reactions of cinnamylamides of ethenetricarboxylate in sequential processes have been studied. Reaction of 1,1-diethyl 2-hydrogen ethenetricarboxylate and trans-cinnamylamines in the presence of EDCI/HOBt/Et₃N led to pyrrolidine products in one pot, via intramolecular [2 + 2], [4 + 2], and some other cyclizations. The types of the products depend on the substituents on the benzene ring and the reaction conditions. Reaction of cinnamylamines without substituents on the benzene ring and with halogens and OMe on the para position at room temperature gave cyclobutane-fused pyrrolidines as major products via [2 + 2] cycloaddition. The reaction at 80 °C in 1,2-dichloroethane gave δ-lactone fused pyrrolidines as major products, probably via ring-opening of the cyclobutanes. Interestingly, reaction of 1,1-diethyl 2-hydrogen ethenetricarboxylate and cinnamylamines bearing electron-withdrawing groups such as NO₂, CN, CO₂Me, CO₂Et, and CF₃ on ortho and para positions in the presence of EDCI/HOBt/Et₃N at room temperature or at 60-80 °C gave tetrahydrobenz[f]isoindolines via [4 + 2] cycloaddition as major products. DFT studies have been performed to explained the observed [2 + 2]/[4 + 2] selectivity.

An unexpected Lewis acid catalyzed Diels-Alder cycloaddition of aryl allenes and acrylates

An unexpected [4+2] cycloaddition of aryl allenes and simple acrylate derivatives is reported. This process functions well with a variety of allenes and acrylates to generate bi- and tricyclic dihydronaphthalene derivatives through a nonconventional bond disconnection.

Cyclopenta[b]naphthalene cyanoacrylate dyes: synthesis and evaluation as fluorescent molecular rotors

We describe the design, synthesis and fluorescent profile of a family of environment-sensitive dyes in which a dimethylamino (donor) group is conjugated to a cyanoacrylate (acceptor) unit via a cyclopenta[b]naphthalene ring system. This assembly satisfies the typical D-π-A motif of a fluorescent molecular rotor and exhibits solvatochromic and viscosity-sensitive fluorescence emission. The central naphthalene ring system of these dyes was synthesized via a novel intramolecular dehydrogenative dehydro-Diels-Alder (IDDDA) reaction that permits incorporation of the donor and acceptor groups in variable positions around the aromatic core. A bathochromic shift of excitation and emission peaks was observed with increasing solvent polarity but the dyes exhibited a complex emission pattern with a second red emission band when dissolved in nonpolar solvents. Consistent with other known molecular rotors, the emission intensity increased with increasing viscosity. Interestingly, closer spatial proximity between the donor and the acceptor groups led to decreased viscosity sensitivity combined with an increased quantum yield. This observation indicates that structural hindrance of intramolecular rotation dominates when the donor and acceptor groups are in close proximity. The examined compounds give insight into how excited state intramolecular rotation can be influenced by both the solvent and the chemical structure.

Hydrazone-palladium catalyzed annulation of 1-allyl-2-bromobenzene derivatives with internal alkynes

Annulation of 1-allyl-2-bromobenzene derivatives with internal alkynes using a hydrazone-palladium catalyst system proceeded smoothly and gave the corresponding polysubstituted naphthalene derivatives in good to high yields.

Divergent Gold(I)-Catalyzed Skeletal Rearrangements of 1,7-Enynes

The gold(I) complex catalyzed cycloisomerization and skeletal rearrangement of 1,n-enynes (n=5-7) is a powerful methodology for the efficient synthesis of complex molecular architectures. In contrast to 1,6-enynes, readily accessible homologous 1,7-enynes are largely unexplored in such transformations. Here, the divergent skeletal rearrangement of all-carbon 1,7-enynes by catalysis with a cationic gold(I) complex is reported. Depending on electronic and steric factors, differently substituted 1,7-enynes react via different carbocations formed from a common gold carbene intermediate to yield on the one hand novel exocyclic allenes and on the other hand tricyclic hexahydro-anthracenes through a novel dehydrogenative Diels-Alder reaction.

Phosphine-Mediated Iterative Arene Homologation Using Allenes

A PPh3-mediated multicomponent reaction between o-phthalaldehydes, nucleophiles, and monosubstituted allenes furnishes functionalized non-C2-symmetric naphthalenes in synthetically useful yields. When the o-phthalaldehydes were reacted with 1,3-disubstituted allenes in the presence of PPh2Et, naphthalene derivatives were also obtained in up to quantitative yields. The mechanism of the latter transformation is straightforward: aldol addition followed by Wittig olefination and dehydration. The mechanism of the former is a tandem γ-umpolung/aldol/Wittig/dehydration process, as established by preparation of putative reaction intermediates and mass spectrometric analysis. This transformation can be applied iteratively to prepare anthracenes and tetracenes using carboxylic acids as pronucleophiles.

Intramolecular didehydro-Diels-Alder reaction and its impact on the structure-function properties of environmentally sensitive fluorophores

Reaction discovery plays a vital role in accessing new chemical entities and materials possessing important function.1 In this Account, we delineate our reaction discovery program regarding the [4 + 2] cycloaddition reaction of styrene-ynes. In particular, we highlight our studies that lead to the realization of the diverging reaction mechanisms of the intramolecular didehydro-Diels-Alder (IMDDA) reaction to afford dihydronaphthalene and naphthalene products. Formation of the former involves an intermolecular hydrogen atom abstraction and isomerization, whereas the latter is formed via an unexpected elimination of H2. Forming aromatic compounds by a unimolecular elimination of H2 offers an environmentally benign alternative to typical oxidation protocols. We also include in this Account ongoing work focused on expanding the scope of this reaction, mainly its application to the preparation of cyclopenta[b]naphthalenes. Finally, we showcase the synthetic utility of the IMDDA reaction by preparing novel environmentally sensitive fluorophores. The choice to follow this path was largely influenced by the impact this reaction could have on our understanding of the structure-function relationships of these molecular sensors by taking advantage of a de novo construction and functionalization of the aromatic portion of these compounds. We were also inspired by the fact that, despite the advances that have been made in the construction of small molecule fluorophores, access to rationally designed fluorescent probes or sensors possessing varied and tuned photophysical, spectral, and chemical properties are still needed. To this end, we report our studies to correlate fluorophore structure with photophysical property relationships for a series of solvatochromic PRODAN analogs and viscosity-sensitive cyanoacrylate analogs. The versatility of this de novo strategy for fluorophore synthesis was demonstrated by showing that a number of functional groups could be installed at various locations, including handles for eventual biomolecule attachment or water-solubilizing groups. Further, biothiol sensors were designed, and we expect these to be of general utility for the study of lipid dynamics in cellular membranes and for the detection of protein-binding interactions, ideal applications for these relatively hydrophobic fluorophores. Future studies will be directed toward expanding this chemistry-driven approach to the rational preparation of fluorophores with enhanced photophysical and chemical properties for application in biological systems.

Diversity-Oriented Approaches to Polycyclics and Bioinspired Molecules via the Diels-Alder Strategy: Green Chemistry, Synthetic Economy, and Beyond

We describe diverse approaches to various dienes and their utilization in the Diels-Alder reaction to produce a variety of polycycles. The dienes covered here are prepared by simple alkylation reaction or via the Claisen rearrangement or by enyne metathesis of alkyne or enyne building blocks. Here, we have also included the Diels-Alder chemistry of dendralenes, a higher analog of cross-conjugated dienes. The present article is inclusive of o-xylylene derivatives that are generated in situ starting with benzosultine or benzosulfone derivatives. The Diels-Alder reaction of these dienes with various dienophiles gave diverse polycyclic systems and biologically important targets.

Exploiting translational stalling peptides in an effort to extend azithromycin interaction within the prokaryotic ribosome nascent peptide exit tunnel

The ribosome is the primary protein synthesis machine in the cell and is a target for treatment of a variety of diseases including bacterial infection and cancer. The ribosomal peptide exit tunnel, the route of egress for the nascent peptide, is an inviting site for drug design. Toward a rational engagement of the nascent peptide components for the design of small molecule inhibitors of ribosome function, we designed and disclosed herein a set of N-10 indole functionalized azithromycin analogs. The indole moiety of these compounds is designed to mimic the translation stalling interaction of SecM W155 side-chain with the prokaryotic (Escherichia coli) ribosome A751 residue. Many of these N-10 functionalized compounds have enhanced translation inhibition activities against E. coli ribosome relative to azithromycin while a subset inhibited the growth of representative susceptible bacteria strains to about the same extent as azithromycin. Moreover, the inclusion of bovine serum in the bacterial growth media enhanced the anti-bacterial potency of the N-10 functionalized azithromycin analogs by as high as 10-fold.

CuO/I2-mediated intramolecular annulation for the synthesis of 2-aroyl-3-hydroxy-4-iodonaphthalenes

A novel method for the direct synthesis of 2-aroyl-3-hydroxy-4-iodonaphthalenes has been developed via CuO/I₂-mediated domino reactions.

Intramolecular dehydro-Diels-Alder reaction affords selective entry to arylnaphthalene or aryldihydronaphthalene lignans

Intramolecular dehydro-Diels-Alder (DDA) reactions are performed affording arylnaphthalene or aryldihydronaphthalene lactones selectively as determined by choice of reaction solvent. This constitutes the first report of an entirely selective formation of arylnaphthalene lactones utilizing DDA reactions of styrene-ynes. The synthetic utility of the DDA reaction is demonstrated by the synthesis of taiwanin C, retrohelioxanthin, justicidin B, isojusticidin B, and their dihydronaphthalene derivatives. Computational methods for chemical shift assignment are presented that allow for regioisomeric lignans to be distinguished.