Search

Design and development of first synthetic approach to the functionalized tetracyclic framework of structurally novel seco -tetracenomycin natural products saccharothrixones A–C has been reported. A thermal dehydro Diels-Alder reaction of an arenyne-alkyne unit has been utilized as the key synthetic step. This strategy has been extended for the generation of a small library of diversely functionalized tetracyclic systems of seco -tetracenomycins. An approach for the synthesis of poly-hydroxyl tetracyclic system has also been described. This report represents the first synthetic approach to the tetracenomycin natural products saccharothrixones A–C. [ABSTRACT FROM AUTHOR]

Abstract: The synthesis of pyridine and bipyridine derivatives of m-carborane via aza Diels–Alder reaction of 1,2,4-triazines with 9-allyl m-carborane and their structural characterization and photophysical properties are described. The products 3- and 4-(m-carborane-9-ylmethyl)-2,2′-bipyridines form Zn(II) complexes on reaction with ZnCl2, which increases significantly their fluorescence intensity. [Copyright &y& Elsevier]

Abstract: The first organocatalytic oxa-Diels–Alder reaction of acyclic α,β–unsaturated ketones with aldehydes is described. This reaction represents a highly chemo- and diastereoselective synthesis of substituted tetrahydropyran-4-ones in good yields with dr up to >95:5. [Copyright &y& Elsevier]

Abstract: Stable, organic solvent soluble bis- and tetrakis-oxadisilole fused pentacenequinones (5a–b) and heptacenequinones (11a–b) were synthesized. Double Diels–Alder and fourfold aldol-condensation approaches were used. Absorption, emission and fluorescence quantum yield of the previously unknown acenequinones 5a and 11a were characterized. The role of the oxadisilole substituent on the photophysical properties was addressed. [Copyright &y& Elsevier]

Abstract: The normal electron-demand Diels–Alder reactions between substituted selenophenes, nitro being one of these groups, and dienes of diverse reactivity give benzoselenophenes derivatives. [Copyright &y& Elsevier]

Abstract: The transannular Diels–Alder (TADA) reaction was applied to the synthesis of the CDE ring system of nakiterpiosin (1). Tetracyclic compound 25 may be a key intermediate in the total synthesis of 1. [Copyright &y& Elsevier]

Abstract: Two unique bisisomalabaricanes jaspolides G (1) and H (2) were isolated from the marine sponge Jaspis sp. Their structures were elucidated on the basis of extensive spectroscopic data (IR, MS, and 1D and 2D NMR) analyses. A possible biogenetic pathway via Diels–Alder dimerization for jaspolides G and H was also proposed. [Copyright &y& Elsevier]

Abstract: Z-Ligustilide, a naturally occurring phthalide isolated from Ligusticum porteri, underwent Diels–Alder reactions with different dienophiles yielding novel tricyclic products with potentially interesting biological properties. Where selectivity was possible, the reactions performed showed regio- and stereoselectivity. The experimental results with ethyl acrylate were compared with the selectivity predicted by ab initio calculations. [Copyright &y& Elsevier]

Abstract: A domino Wittig Diels–Alder reaction has been employed in delineating a short and flexible synthetic stratagem for ready access to the AB ring system and the tricyclic framework of furanosesquiterpenes, such as the bioactive natural products, furodysin and furodysinin. [Copyright &y& Elsevier]

Abstract: Acyclic conjugated (E,Z,E,E)-tetraenes, upon thermolysis, undergo a domino pericyclic process involving 6π electrocyclisation of the (E,Z,E)-triene moiety to give the corresponding cis-disubstituted 5-vinyl-1,3-cyclohexadienes, followed by an intramolecular Diels–Alder reaction with the vinyl side chain to give tricyclo[3.2.1.02,7]oct-3-enes. [Copyright &y& Elsevier]

Abstract: The ethylidene acetal of d-erythrose was used as a template for stereoselective IMDA reactions: high endo selectivity and yields in favor of the cis product were observed with 1,3,9-trienes, resulting from a boat transition state. For natural product synthesis, the reaction was successfully applied to a diene with terminal Z-olefin. [Copyright &y& Elsevier]

Abstract: Knoevenagal condensation of indole-2-carbaldehyde containing an internal dienophile with coumarins, followed by domino intramolecular hetero Diels–Alder reaction, provides polycyclic heterocycles. Different approaches for stereo- and chemoselective synthesis of indolo[2,1-a]pyrrolo[4′,3′:4,5]pyrano[5,6-c]coumarin and indolo[2,1-a]pyrrolo[4′,3′:4,5]pyrano[6,5-c]chromone derivatives are described. [Copyright &y& Elsevier]

Abstract: Intramolecular ionic Diels–Alder reaction of 2-methyl-3,9,11-tridecatriene-2-ol (1) was studied under acidic conditions. Treatment of 2-methyl-3,9,11-tridecatriene-2-ol (1) with trifluoromethanesulfonic acid yielded 7-methyl-8-isopropenyl-1,2,3,4,4aR ∗,7R ∗,8R ∗,8aS ∗-octahydronaphthalene (4) and (1Z)-1-((E)-but-2-enylidene)-2-(2-methylpropenyl)cyclohexane (5) through regioselective intramolecular ionic Diels–Alder reaction. The reaction appeared to proceed partly through a stepwise mechanism involving a carbocation intermediate. However, a concerted pathway rather than a stepwise one is suggested to be involved in the acid-catalyzed intramolecular Diels–Alder reaction of 2,11-dimethyl-1,3,9,11-dodecatetraene (13). [Copyright &y& Elsevier]

Abstract: Chiral fluorous imidazolidinone catalyst 2 provides consistently high enantioselectivities in Diels–Alder reactions of dienes and α,β-unsaturated aldehydes. The catalyst can be readily separated from the reaction products by fluorous solid-phase extraction, and recovered in excellent purity for direct reuse. [Copyright &y& Elsevier]

Abstract: The antimalarial robustadials A and B have been synthesized in two steps starting from commercially available phloroglucinol comprising a key biomimetic three-component reaction that involves in situ generation of an o-quinone methide via Knoevenagel condensation and subsequent Diels–Alder cycloaddition with (−)-β-pinene. [Copyright &y& Elsevier]

Abstract: A new route to various medium ring heterocycle-annulated tetra-, penta- and hexacyclic carbazole derivatives has been developed using successive applications of three atom economic processes, viz. Claisen rearrangement, olefin metathesis and Diels–Alder reactions. [Copyright &y& Elsevier]

Abstract: Antimony trichloride (SbCl3) was found to be an efficient catalyst for the inverse electron demand imino Diels–Alder reactions of in situ generated N-benzylidenes with 3,4-dihydro-2H-pyran and 2,3-dihydrofuran to afford pyrano and furano[3,2-c]quinolines in excellent yields. [Copyright &y& Elsevier]

Abstract: A series of dendritic ligands with a 2,2′-bipyridine core was synthesized through the coupling of 4,4′-dihydroxy-2,2′-bipyridine with poly(arylether) dendron in fair yields. The corresponding copper(II) trifluoromethanesulfonate (triflate) dendrimers were applied as a Lewis acid catalyst to the Diels–Alder reaction. A positive dendritic effect on the chemical yields of adducts was observed. [Copyright &y& Elsevier]

Abstract: A highly efficient method for the synthesis of 1,2,3,4-tetrahydroquinoline derivatives via a molecular iodine catalyzed domino reaction of anilines with cyclic enol ethers, such as 2,3-dihydrofuran and 3,4-dihydro-2H-pyran, is described. The reaction may proceed through an aza-Diels–Alder process between an in situ generated 2-azadiene and another equivalent of cyclic enol. [Copyright &y& Elsevier]

Abstract: 2,5-Bis(methoxycarbonyl)-3,4-diphenylcyclopentadienone (1a) reacts with prop-2-yn-1-ols (2) to give 3-methylene-2,3,3a,6a-tetrahydrocyclopenta[b]furan-4-one derivatives in the presence of trialkylamines. [Copyright &y& Elsevier]

Abstract: The hetero-Diels–Alder reactions of enolic ethers generated from methylenation of various esters are described, which allow for the rapid synthesis of various substituted [6,6] aromatic spiroketal skeletons. [Copyright &y& Elsevier]

Abstract: An efficient synthesis of spiroannulated dihydroisobenzofurans is achieved using easily accessible carbohydrate-derived furanyl propargyl ethers via an AuCl3 promoted intramolecular Diels–Alder (IMDA) reaction. The scope of the spiroannulation protocol was demonstrated using a diverse range of pentofuranosyl, hexofuransoyl and hexopyranosyl derived substrates in order to synthesize spiroannulated dihydroisobenzofurans. The reaction is high yielding, moisture tolerant, fast and uses only a catalytic amount of AuCl3. [Copyright &y& Elsevier]

Abstract: An efficient strategy for the synthesis of functionalized 2,2′-bipyridines is reported. The strategy is based on readily available 3-pyridyl-1,2,4-triazine 4-oxides and uses a reaction sequence of nucleophilic substitution of hydrogen and aza Diels–Alder reaction. [Copyright &y& Elsevier]

Abstract: Three approaches towards the synthesis of the 1,7-dihydropyrano[2,3-g]indole ring system of the stephacidins, paraherquamides and norgeamides have been investigated. The first involves a tandem nitrene insertion/aromatic Claisen rearrangement. The second consists of a more conventional approach from commercially available 6-benzyloxyindole. The third approach is a revised synthesis of the 2-prenylated pyrano indole necessary for a biomimetic Diels–Alder approach towards the stephacidins, aspergamides and the norgeamides. [Copyright &y& Elsevier]

Abstract: A frontier demarcating superelectrophilic compounds that undergo both Diels–Alder reactivity and σ-complexation reactions, from traditional electrophiles, is afforded through the thermodynamic tendency for σ-complexation as defined by the pK a values for H2O addition to electron-deficient aromatic and heteroaromatic substrates. [Copyright &y& Elsevier]

Abstract: The first total synthesis of acutifolone A, a sesquiterpenoid carrying the bicyclo[4.3.0]nonane structure 1 , was successfully achieved from the intermediate 6 produced by the intramolecular Diels–Alder reaction. [Copyright &y& Elsevier]

Abstract: Based on a heterocyclic Diels–Alder strategy, a concise synthesis of 5-aza-analogues of angucyclines bearing a 2-deoxy-C-glycoside subunit is reported. Starting from a common intermediate, a peracetylated D-2-deoxyglucose could be linked to carbons C9 or C10 of the tetracyclic framework. Further manipulations of the sugar residue allowed the installation of bromo and azido substituents at carbon C6′. [Copyright &y& Elsevier]

Abstract: An efficient route to a new class of indole derivatives, tetrahydrochromeno[2,3-b]carbazoles, has been developed. The cycloaddition reactions of chromone-3-carboxaldehydes with indole-o-quinodimethane gave a diastereomeric mixture of Diels–Alder cycloadducts in good yields after in situ deformylation. [Copyright &y& Elsevier]

Abstract: The Diels–Alder reaction of the acrylate derived from levoglucosenone with cyclopentadiene was studied under several conditions, in the presence and absence of a Lewis acid. The results showed satisfactory diastereomeric excess and the ratio of cycloadducts was found to depend on the reaction conditions. A reversal in stereoselectivity was observed when EtAlCl2 or Et2AlCl were employed as Lewis acids. [Copyright &y& Elsevier]

Abstract: Diels–Alder reactions in a solid state between anthracene (AN) derivatives and p-benzoquinone (BQ) under mechanical stressing are accelerated by adding a catalytic amount of 2-naphthol (NP) or (rac)-1,1′-bis-2-naphthol (BN). Their catalytic effects are based on the formation of the charge transfer complex with strong hydrogen bonds. BN is capable of incorporating BQ together with its reaction partner, AN derivatives, simultaneously. The resulted molecular complex with BN provides crystallographically ordered homogenic reaction fields, resulting in the higher rates of the present solid state Diels–Alder reaction. [Copyright &y& Elsevier]

Abstract: A highly regio- and stereoselective Brønsted acid-catalyzed coupling of ynamides and indoles is described. This process is the equivalent of hydroarylation of ynamides and leads to the efficient syntheses of vinylindoles. Diels–Alder reaction between the vinylindoles and DMAD afforded carbazole derivatives in good yields. [Copyright &y& Elsevier]

Abstract: Diversity-oriented organic synthesis (DOS) is a key concept for construction of skeletally diverse small molecule libraries to discover drug-like small molecules. Here, we describe a DOS class to transform a complex 7-oxanorbornene skeleton, which is readily accessible by a tandem Ugi/Diels–Alder reaction, into two heterotricycle skeletons selectively by using tandem ROM/CM/RCM reaction. In the present study, the mode of cyclization is pre-encoded by building blocks used in the complexity-generating tandem Ugi/Diels–Alder reaction. Since variable alkenes can be used in the CM reaction, our approach can be extended to construct both skeleton- and appendage-diverse small molecule libraries. [Copyright &y& Elsevier]

Abstract: The enantioselective Diels–Alder reactions of 1-phenoxycarbonyl-1,2-dihydropyridine with 1-alkylated acryloyl-pyrazolidin-3-ones using chiral cationic palladium–phosphinooxazolidine (Pd–POZ) catalyst afforded chiral isoquinuclidines with excellent enantioselectivity (up to 97% ee). [Copyright &y& Elsevier]

Abstract: New asymmetric bis(oxazoline) (Box) ligand bearing amide group at the oxazoline 4-position, (S,S)-2,2′-methylenebis(4-tert-butylcarbamoyl-2-oxazoline) ( 1S ), was designed and synthesized for selective catalytic reaction. The crystal structure of the ternary copper complex, consisting of 1S and N-benzoyl-N-phenyl-hydroxylamine, demonstrated interligand interactions, such as hydrogen bonding and CH-π interaction. Catalytic performance of the copper complex with 1S was investigated for an asymmetric Diels–Alder reaction using benzylidene-2-acetylpyridine and 1,3-cyclohexadiene (CHD). The reaction product was enantio-pure endo-(pyridin-2-yl)(3-phenylbicyclo[2,2,2]oct-5-ene-2-yl)methanone (BPCD), of which crystal structure was analyzed by the X-ray method. No stereo- and enantio-isomer of BPCD was detected by chiral HPLC analysis. Introduction of hydrogen bonding site into 1S can promote the Diels–Alder reaction even though using poor reactive CHD. Without 1S , this reaction did not give any product. Addition of 2-propanol to this reaction system inhibited the formation of BPCD, indicating that the designed interligand interaction sites, especially hydrogen bonding, play an important role for catalytic performance. [Copyright &y& Elsevier]

Abstract: The synthesis and X-ray structural determination of vinylogous tetrathiafulvalenes (TTFV) bearing functional groups on the central conjugation are reported. An unexpected evolution of the bis hydroxymethyl TTFV leading to a derivative, which acts simultaneously as a diene and a dienophile in a Diels–Alder reaction is also described. [Copyright &y& Elsevier]

Abstract: Reaction of 4-lithio-4-(phenylsulfonyl)cyclopentene with an l-tryptophan-derived N-tosylaziridine provides an adduct. Oxidative cleavage of the cyclopentene double bond provides a dialdehyde, which enters into acid-catalysed Pictet–Spengler-type bicyclisation to give a tetracyclic aldehyde. Completely regioselective silyl dienol ether formation followed by completely stereoselective hetero-Diels–Alder reaction with monomeric formaldehyde gives a late-stage intermediate in a planned total synthesis of the macroline-related alkaloid (−)-alstonerine. [Copyright &y& Elsevier]

Abstract: The fluorescence of a pyrene-arylmaleimide dyad and its Diels–Alder adduct can be thermally modulated through reversible Diels–Alder reaction of arylmaleimide unit with furan. Moreover, the fluorescence intensities of the Diels–Alder adduct of dyad 1 with furan vary linearly with the temperatures of the corresponding solutions, demonstrating that these molecules are interesting compounds for studies of fluorescent molecular thermometers. [Copyright &y& Elsevier]

Abstract: The bicyclo[4.3.0]nonane (C11–C21) fragment of stawamycin has been prepared by a sequence involving 11 steps (10% overall yield) from methyl (R)-(−)-3-hydroxy-2-methylpropionate. Key steps are a Pd-catalysed Stille coupling reaction between a vinyl iodide and a vinyl stannane followed by an intramolecular Diels–Alder cycloaddition reaction to give the desired adduct as the major isomer in 21% overall yield. [Copyright &y& Elsevier]

Abstract: Newly introduced chiral ‘roofed’ 2-thiazolines, prepared from sterically congested, conformationally rigid chiral 2-aminothiols, function as efficient chiral ligands for the asymmetric Diels–Alder reaction of cyclopentadiene and 3-acryloyl-2-oxazolidinone. [Copyright &y& Elsevier]

Abstract: The reaction of indoloazepines 1 and α,β-unsaturated aldehydes in reflux toluene led to tetracyclic compounds 2. The key to this reaction was an intramolecular Diels–Alder cycloaddition by the indoloacrylate (dienophile)–dienamine (diene) intermediates generated in situ. [Copyright &y& Elsevier]

Abstract: The asymmetric Diels–Alder reactions of dichlorovinylborane and vinyl-9-BBN with two chiral dienes have been studied theoretically. Calculations suggest high reactivity and regio- and stereoselectivity could be achieved in these processes giving the anti para endo product. This class of reactions represents a potential stereoselective approach to a variety of chiral carbocycles. [Copyright &y& Elsevier]

Utilising an intermediate prepared by an intramolecular acylnitroso Diels–Alder reaction, a suitably protected right hand part of AI-77-B was synthesised in racemic form. A modified procedure for introducing an Aoc (tert-amyloxycarbonyl) protecting group is discussed. [Copyright &y& Elsevier]

A new diastereoselective approach to oxygenated spongiane diterpenes starting from (R)-(−)-carvone is described. The carvone is incorporated as the B ring in the final spongiane framework using a B→AB→ABC→ABCD approach, which involves an intramolecular Diels–Alder reaction and the regioselective ring-opening of a dihydrofuran ring as key synthetic steps. The structure of the key intermediate in this approach has been verified by X-ray crystallography. [Copyright &y& Elsevier]

Electron-donating substituted 3-cyanomethyl-2-vinylindoles were found to rearrange via thermal [1,5]H shift into the corresponding indole-2,3-quinodimethanes which were trapped by dienophiles to afford tetrahydrocarbazoles. [Copyright &y& Elsevier]

The imine Ph2CHN&z.dbnd6;CHCO2Et, generated from benzhydrylamine and ethyl glyoxylate, provides a Diels–Alder adduct with 1,3-pentadiene from which a range of cis-2,6-disubstituted piperidines can be accessed; the benzhydryl group confers high diastereocontrol for derivatising the six-membered ring, allowing access to 2,5,6-trisubstituted piperidines, and to 2,6-disubstituted piperidines such as pinidine. [Copyright &y& Elsevier]

The imine Ph2CHN&z.dbnd6;CHCO2Et, generated from benzhydrylamine and ethyl glyoxylate, is an excellent dienophile in aza-Diels–Alder reactions, giving diastereomerically pure cycloadducts in high yield. [Copyright &y& Elsevier]

The synthesis of highly functionalized oxabicyclo[2.2.1]heptadiene derivatives through the sequential use of an Ugi or Passerini multi-component coupling reaction followed by an intramolecular acetylene/furan Diels–Alder reaction was investigated. The nature of the heteroatom in the tether was determined to play a critical role. [Copyright &y& Elsevier]

2(1H)-Pyrazinones were converted into [3,4-b] and [3,4-c] sulfolene pyridinones 4 and 5, serving as precursors for the corresponding 3,4- and 5,6-dimethylene 2(1H)-pyridinone ortho-quinodimethanes. These were trapped by in situ reaction with dienophiles. Tethering of 4 also enabled intramolecular cycloaddition. [Copyright &y& Elsevier]

Abstract: The initial inverse electron-demand hetero-Diels–Alder reaction of N-sulfonyldivinylmethanimine with electron-rich dienophiles (ethyl vinyl ether and ethyl vinyl sulfide) affords [4+2] cycloadducts with high endo selectivity. The monocycloadducts then undergo a second Diels–Alder reaction on the newly formed diene unit with electron-deficient dienophiles (tetracyanoethylene, 4-phenyl-1,2,4-triazoline-3,5-dione, and N-phenylmaleimide) to give highly stereoselectively the crossed biscycloadducts, hexa- and octahydroquinolines, and octahydropyridopyridazines. [Copyright &y& Elsevier]

• endo -1-Phenylborneol 1a bears the under-explored benzocamphor scaffold. • 1a was obtained from economic starting materials avoiding the use of toxic reagents. • 1a was evaluated as a chiral auxiliary in asymmetric aza-Diels Alder reactions. • 1a induces diastereomeric excesses comparable to (−)-8-phenylmenthol. We report the synthesis and preliminary evaluation of (1S,2S,4R)-7,7-dimethyl-1-phenylbicyclo[2.2.1]heptan-2-ol 1a , which was obtained in 3 steps from inexpensive starting materials, as a chiral auxiliary. The potential for asymmetric induction was investigated by carrying out aza-Diels-Alder reactions with cyclopentadiene and imine derivatives of 1a from (R)-(+)-1-phenylethylamine, (S)-(−)-1-phenylethylamine and benzylamine. The results showed marked exo selectivity and good diastereoisomeric excess when 1a was combined with (R)-(+)-1-phenylethylamine. These results are comparable with those reported using (−)-8-phenylmenthol, suggesting that 1a can represent an economically viable alternative to current chiral auxiliaries. [ABSTRACT FROM AUTHOR]