Diels-Alder Products Research Articles

Iristectorones A-H, spirotriterpene-quinone adducts from Iris tectorum

Eight tetracyclic spirotriterpene derivatives, iristectorones A-H, have been found in the seeds of Iris tectorum. Their structures were established to be the Diels-Alder products of 2-methoxy-6-[( Z)-10-pentadecenyl]- p-benzoquinone with triterpenic conjugated trienes having spiro [4.5] decane skeleton derived from iristectorenes A-H, respectively, on the basis of spectral methods and chemical transformations. A possible biogenetic route for these esters has been also discussed.

Synthesis of (±)-conduramines from pyrrole

The Diels-Alder product 1b, of tosylacetylene and N- tert-Boc-pyrrole, was converted into (±)-conduramine C-1 ( 22) and the tetraacetates of (±)-conduramine A-1 ( 9b) and F-1 ( 15b).

Einfache Synthese von 2,2-Diethoxy-2,5-dihydrofuranen, 2(5 H)Furanonen und 2-Ethoxy-furanen.Kristall-und Molekülstruktur eines Barrelenon Diels-Aider Produktes [1] / Convenient Synthesis of 2,2-Diethoxy-2,5-dihydrofurans, 2(5 H)Furanones and 2-Ethoxyfurans.Crystal and Molecular Structure of a Barrelenone Diels-Alder Product [1

Abstract Reaction of 1,2-hydroxyketones 5 with (2,2-diethoxyvinylidene)triphenylphosphorane (2) or (2,2-diethoxyvinyl)triphenylphosphonium tetrafluoroborates 6 yields the 2,2-diethoxy- 2.5-dihydrofurans 9. Depending on the reaction conditions used, the orthoesters 9 can be hydrolized to give 2(5 H)furanones 10 and 2-ethoxyfurans 11, respectively. 4,5-Dimethyl- 5.6-dihydro-2-pyranone (20) and 8-methoxycoumarin (23) are prepared, starting from (2,2-diethoxyvinyl)triphenylphosphonium tetrafluoroborate (6 a) and 1-hydroxy-2-methyl- 3-butanone (16) or 2-hydroxy-3-methoxy-benzaldehyde (21). The 2-ethoxyfuranes 11 readily undergo Diels-Alder reactions with 2-chloracrylonitrile (24), maleic anhydride (26), N-phenyl-1,2,4-triazoline-3,5-dione (28) and dimethyl acetylenedicarboxylate (30) to give the corresponding Diels-Alder products 25, 27, 29 and 31, respectively. Contrary to 2-ethoxyfuran 11b , 11a reacts with two equivalents of acetylene 30, to yield barrelenone 34. The structure of 34 unequivocally is established by X-ray structure analysis.

Competing Reactions of Silenes: [2+2], [4+2], and [6+2] Cycloadditions with Cycloheptadiene and Cycloheptatriene

Silabicyclo[4.2.1]nonadienes 3 are two of the products of the reaction of silene 1 and cycloheptatriene. Besides these unusual[6 + 2] cycloadducts, the [2 + 2] cycloadducts also arise, which isomerize into 3 upon heating. The [4 + 2] and [2 + 2] adducts of 1,3-cycloheptadiene and 1 form competitively; the [2 + 2] cycloadducts rearrange to give the Diels–Alder products.

Cycloadditionen. 23 [1]. Zur Thermischen Reaktivit�t von S-(1-Naphthyl)- und S-(9-Anthryl)-2-methyl-buta-2,3-dienthios�ureestern

Cycloadditions. 23. The Thermal Reactivity of S-(1-Naphthyl) and S-(9-Anthryl)2-methyl-2,3-butadienethioates Heating of the S-(1-naphthyl)esters of 2-methyl-2,3-butadiene thioacid and of 2-methyl-4,4-diphenyl-2,3-butadiene thioacid (3a resp. 3b) furnishes mixtures of the Diels-Alder products 5a, b and the cyclobutenone 7 and the naphthol derivative 8, resp. The corresponding S-(9-anthryl) esters 4a, b are not isolable; under the conditions of their synthesis (allenecarboxylic acids 1a u. b, 9-thioanthrol 2b, DCC and DMAP) they isomerise spontaneously to the Diels-Alder products 9.

Unusual functionalization of C60via hydrozirconation: reactivity of the C60–ZrIVcomplex vs. alkyl–ZrIVcomplexes

The reaction of the C60 hydrozirconation adduct 1 with N-bromosuccinimide and m-chloroperbenzoic acid leads to the formation of Diels–Alder products with bromo- and hydroxy-cyclopentadiene, respectively.

A Study of the Hetero Diels-Alder Reaction of N-Alkyl-2-cyano-1-azadienes with 2-Vinylindole

The N-alkyl-2-cyano-1-azadienes (2a) and (2b) derived from ethanolamine react with 2-vinylindole under thermal conditions to give the Michael addition adducts (9) and (9') as the principle product. In the reacaon of 2a with vinylindole the DielsAlder product (11) was also isolated. In the reaction with 2b, formation of compounds (9) was accompanied by the cyclized product (10) and the Diels-Alder adduct (13)

Synthesis and reactions of achiral 3-substituted vinylketene acetals as dienes in the Diels-Alder reaction

The synthesis of three new vinylketene acetals, each bearing a heteroatom substituent at C3 of the diene unit, and their reactions with representative dienophiles in Diels-Alder reactions are presented. All the dienes react well at room temperature, indicating substantial activation of the cycloaddition event. The stereochemistry of the major Diels-Alder product of a 3-SPh-substituted vinylketene acetal is opposite to that produced by the corresponding 3-unsubstituted compound.

Cycloaddition Reactions Initiated by Photochemically Excited Pyrylium Salts

AbstractSeveral pyrylium, thiapyrylium, and pyridinium salts have been synthesized and used as sensitizers for photochemically induced electron‐transfer (PET) reactions. The salts have been tested in the mixed cycloaddition reactions of styrenes 9 with 1,3‐cyclohexadiene (8) or 1,1'‐dicyclohexenyl (23). In the case of the PET [4 + 2] cycloaddition of styrene (9a) to 1,3‐cyclohexadiene (8), the reaction takes place via the cation radical of the diene. When chloroform instead of dichloromethane is used as the solvent, only [2 + 2] cycloaddition products are obtained. In contrast, if 1,3‐cyclohexadiene (8) is replaced by 1,1'‐dicyclohexenyl (23), the key step of the reaction seems to be the oxidation of styrene (9). The product ratios depend on the sensitizers used. If solvent‐separated ion pairs are formed, styrene reacts as diene to give 1‐cyclohexenyloctahydro‐phenanthrene derivatives 28; cycloaddition via contact ion pairs leads to the Diels‐Alder product with styrene acting as the dienophile.

An Unexpected Tandem Reaction between N-Butadienyl-N-alkylketene N,O-Trimethylsilylacetals of Propionamide and Activated Dienophiles like N-Phenyl-maleimide or Acryloyl Chloride

Starting from the N-butadienyl-N-alkylpropionamides 1a-1c the corresponding N,O-trimethylsilylacetals could be obtained using the mixture of LDA and trimethylsilyl chloride in THF. The unexpected reaction sequence Diels-Alder reaction/acylation between the N-butadienyl-N-alkylketene N,O-trimethylsilylacetal of propionamide (2a-2b) and N-phenylmaleimide produced tricyclic products rac-5a-rac-5b and bicyclic products rac-6a–rac-6b with high diastereoselectivity. The reaction of the N,O-trimethylsilylacetals 2a and 2c with acryloyl chloride in a similar sequence gave the bicyclic products rac-8a and rac-8c. The stepwise synthesis of bicyclic systems of this general structure could only be successfully executed in 26% yield treating the Diels-Alder product rac-10 with LDA.

Ketene-diene [4 + 2] cycloaddition products via cation radical initiated Diels-Alder reaction or vinylcyclobutanone rearrangement

Whereas the thermal reaction of the aryl methyl ketenes 1a and 1b with 2 resulted, as anticipated, in the periselective formation of the vinylcyclobutanones 3-6, the aminium ion salt initiated cycloaddition afforded selectively the Diels-Alder products 10 and 11. The potential role of BrOnsted and Lewis acids, the suitability of different one-electron oxidants, and the effect of reactant concentration, reaction time, and added neutral amines was tested. From the results it is deduced that in the aminium ion salt initiated reaction the diene cation radical reacts with a neutral ketene in a [3+2] cycloaddition

Synthesis, purification, and characterization of the 1 : 1 addition product of C60 and anthracene

A cleanly separated Diels–Alder product of C60, a 1 : 1 adduct of anthracene, has been synthesized and characterized by thermogravimetric analysis, and NMR, UV–VIS, IR and mass spectroscopies.

Silaheterocyclen, XX Aminosubstituierte Vinylchlorsilane und Silaethene: Bausteine zur Synthese von 1,3-Diaza-2-silacyclopentanen / Silaheterocycles, XX Aminosubstituted Vinylchlorosilanes and Silenes: Building Blocks for the Synthesis of 1,3-Diaza-2-silacyclopentanes

The amino-substituted vinylchlorosilanes 4-7 are synthesized from N,N,N′-trimethylethylenediamine (8a) or tris(trimethylsilyl)ethylenediamine (8b), Li Bun and organodichlorovinylsilanes. 5 eliminates trimethylchlorosilane when distilled and yields 1,3-diaza-2-silacyclopentane 9, whereas the compounds 6 and 7 show a great tendency to oligomerize. The reaction of 4 with LiBut gives a neopentylsilene intermediate 10 a which can be trapped by isoprene or 1,3-butadiene yielding small amounts of the Diels-Alder products 11 and 12, respectively. The main reaction pathway for 10 a is rearrangement with migration of a Me3Sigroup from nitrogen to the silene’s carbon atom and a new N—Si bond formation to give the diazasilacyclopentane 10 which has been characterized by X-ray diffraction analysis. This intramolecular rearrangement appears to involve a pentacoordinated silene Si-atom. No dimerisation of 10a to a disilacyclobutane is observed. The introduction of a second Si-tris(trimethylsilyl)ethylenediamine substituent at the SiC frame work does not result in silene stabilisation: there is no evidence for Si-hexacoordination in silene 15 nor in the [4+2] cyclo-addition product with isoprene (14).

Further Studies on Quinone Diels-Alder Reactions with 1,3,3-Trimethyl-2-vinylcyclohexenes: Regioselective Synthesis of 12-Methyl-podocarpane Diterpenes and Isolation of a Hetero Diels-Alder Product from 1,4-Benzoquinone

Abstract Diels-Alder reactions of 2-[(E)-β-alkoxyvinyl]-1,3,3-trimethyl-cyclohexenes with 2-methoxy-3-methyl-1,4-benzoquinone regioselectively produce adducts possessing the 12-methyl-podocarpane ring skeleton. In addition, in the reaction with 1,4-benzoquinone an unusual hetero Diels-Alder product involving the C[dbnd]O group of the quinone is found in low yield.

Silaheterocyclen, XIII Erzeugung und Cycloadditionsverhalten von 1,3-Diaza-2,4-disila-und 1.3-Disilacyclobutanen mit exocyclischer SiC-Doppelbindung Silaheterocycles, XIII / Formation and Cycloaddition Reactions of 1,3-Diaza-2,4-disila-and 1.3-Disilacyclobutanes Containing an Exocyclic SiC Double Bond

The silenes A and B are formed by reacting 1,3-ditbutyl-2,4-dichloro-2,4-divinyl-1,3-diaza- 2.4-disilacyclobutane (2) and 1,3-dichloro-2,4-dineopentyl-1,3-divinyl-1,3-disilacyclobutane (15) with LiBut in n-pentane in the temperature range from −10 to 0 °C. The reaction primarily leads to the corresponding α-lithioadducts (addition of LiBut to the vinyl group of 2 and 15), and with subsequent 1,2-LiCl elimination yields A and B as intermediates. A can be trapped by polar reagents Me3SiX (X = OMe, OSO2CF3) as well as by organic dienes which add across the Si = C bond; in the absence of a trapping agent the spiro compound 6 is isolated. The silenes A and B differ in their cycloaddition behaviour to butadienes, norbornadiene and cyclohexa-1,3-diene: Whereas for A the regioselective [2 + 2]-cycloaddition to yield monosilacyclobutane derivatives is preferred due to electronic reasons, the reaction of B leads mainly to Diels-Alder products. Thus, A is quite comparable in its reactivity to dichloroneopentylsilene, while B reacts like its diorgano substituted analogues R2Si = CHCH2But (R = Me, But or Ph).

Studies on diels-alder reactions of 1,3,3-trimethyl-2-vinylcyclohexene with 2-cyclohexenones

The ZnBr 2-catalyzed reaction of 1,3,3-trimethyl-2-vinylcyclohexene ( 4) with 2-carbomethoxy-4,4-dimethyl-2-cyclohexenone at high pressure (12 kbar) produces the expected Diels-Alder product. However, reactions of ( 4) with the more sterically demanding dienophile ( 5a) give products of apparent Michael reaction followed by proton transfer.

2-Trimethylsilylvinylboranes: highly reactive and selective diels-alder equivalents of 2-trimethylsilylvinyl alcohol and acetylene

The readily available 2-trimethylsilylvinyl-9-BBN ( 1) is a highly reactive and selective dienophile. The Diels-Alder products are easily converted into trimethylsilylcyclohexenols and 1,4-cyclohexadienes.

Base-Induced Addition-Elimination Reactions of Electron-Deficient Vinylarenes Containing a Carbonyl or Ester Group Utilizing 4-Phenyl-3H-1,2,4-triazole-3,5(4H)-dione(PTAD)

Abstract The reaction of electron-deficient vinylarenes such as styrylketones and cinnamate with PTAD afforded double Diels–Alder products and Diels–Alder ene products; the latter underwent novel base-induced elimination of 4-phenyl-1,2,4-triazolidine-3,5-dione via a stable carbanion.

The fluorocontaining diene synthesis products as a potent GABA-antagonists

It is well established that a biological activity of many agro- chemicals may be strongly enhanced by a polyfluorination. In our research we studled a GABA-antagonistic properties of the polyfluorinated compounds (I)–(V) (GABA-γ-aminobutyric acid). ▪ All compounds were obtained from the corresponding dienes and alkenes (I–III) or nitrites (IV–V) as the Diels-Alder products. The biological activity were evaluated by the two methods: i) influence on the GABA-induced chloride [ 36Cl −] uptake in rat brain synaptoneurosomes and ii) influence on the amplitude of the populational spikes in the mice hyppocamp slices. All five compounds performed a pronounced GABA-antagonistic (method 1) and convulsive activities (ii). So (I) and (II) at concentration 0.1 mkM blocked chloride-anion influx to 30% and O% levels (basic) respectevly. (I)–(V) in the concentration-depended manner enhanced an amplitude of the main populational spike up to 150–200% relatively to basic level. A Maximal values of the amplitudes occurred at 1–10 mkM.

Novel base-promoted addition-elimination reaction of electron-deficient benzylidene derivatives with N-phenyl-1,2,4-triazole-3,5-dione (PTAD)

The reaction of electron-deficient benzylidene derivatives with PTAD afforded the double Diels–Alder product and the Diels–Alder ene product; the latter underwent novel base-induced elimination of phenyl urazole via a stable carbanion.