Thermal Diels Research Articles

High pressure and thermal Diels–Alder reactions of 5-nitro[2.2]paracyclophanepyran-6-one

The Diels–Alder reactions of 5-nitro[2.2]paracyclophanepyran-6-one with 1,3-butadienes and 1,2-dihydro-3-vinyl-naphthalene were examined under thermal and high-pressure conditions. The cycloadditions with 1,3-butadienes occurred in good yield and anti- exo diastereoselectively only under high-pressure conditions; the one with 1,2-dihydro-3-vinyl-naphthalene afforded comparable yields of mixtures of anti/ syn adducts under normal and high-pressure conditions. A structural analysis of the reaction products by 1H and 13C NMR spectroscopy is presented.

Stereoselective preparation of γ- and σ-sultams by thermal and high-pressure intramolecular Diels–Alder reaction of vinylsulfonamides

Stereoselective preparation of γ- and σ-sultams by thermal and high-pressure intramolecular Diels–Alder reaction of vinylsulfonamides

Thermal Diels–Alder Reactions of 3‐(Benzoylamino)‐6‐(polyfluoroalkyl)pyran‐2‐ones – New Synthesis of p‐(Polyfluoroalkyl)anilines

AbstractA new practical method for the regioselective synthesis of the N‐benzoyl‐4‐(polyfluoroalkyl)anilines 5a–g by thermal Diels–Alder cycloaddition of 5‐substituted 3‐(benzoylamino)‐6‐(polyfluoroalkyl)pyran‐2‐ones 1a–e with fluorostyrenes 2 and 7, acetylenes 8a–c or vinyl ethers 10 and 13a and 13b is described. In the case of the reactions of pyrone 1a with cyclic vinyl ethers 13a and 13b, the dihydrobenzenes 14a and 14b were obtained. Free 4‐(polyfluoroalkyl)anilines 16a–c were smoothly formed in good yields by DBU‐assisted benzoyl deprotection. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

Stereoselective Synthesis of Substituted Dienes by the Double ortho Ester Claisen Rearrangement.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Generation of Selenoaldehydes via Retro Diels–Alder Reaction and Their Behavior in the Reaction with Some Enophiles

The [4, 2] cycloadducts of selenoaldehydes and anthracene regenerate selenoaldehydes in situ quantitatively under neutral conditions via thermal retro Diels–Alder reaction. The reactions of selenoaldehydes generated by this method with 2-silyloxy-1,3-butadiene, 2-methoxyfuran, and 5-ethoxyoxazoles are described.

Stereoselective synthesis of substituted dienes by the double ortho ester Claisen rearrangement

This letter shows the highly stereoselective synthesis of substituted ( E)-1,3-dienes from substituted propargylic diols via the double ortho ester Claisen rearrangement. The cyclohexyl-substituted diene undergoes thermal Diels–Alder cycloaddition with maleic anhydride to produce the corresponding bicyclic diester in highly stereoselective manner.

Synthesis and Diels–Alder reactions of 9-(4-benzyloxazolin-2-yl) anthracene

The synthesis of 9-(4-benzyloxazolin-2-yl)anthracene is described employing a new approach for the cyclisation of β-hydroxy amides to oxazolines. Thermal Diels–Alder reactions with N-methyl maleimide were found to be considerably slower than those previously observed. Essentially no diastereoselectivity was observed in these reactions as the benzyl stereodirecting group is remote from the reactive site. Minor rate enhancements were noticeable in the presence of some added Lewis acids, but with no diastereoselection.

Synthesis and Reactivity of Z and E Functionalized Allylic Fluorides.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Synthesis and reactivity of Z and E functionalized allylic fluorides

The allylic fluorides 1 and 2 are used as models to study the effect of the allylic C–F bond on the diastereoselectivity of reactions occurring on the vicinal double bond, as well as the compatibility of this C–F bond with various reagents. The configurational stability of the Z double bonds in enals and enones 1 and 3 is noteworthy. This allowed us to perform various types of reactions (including thermal Diels–Alder cycloadditions) on derivatives 1 with full control of the Z geometry.

Synthesis of Cyclopentene‐Fused Pyrroloisoquinolinone Derivative via N‐Acyliminium Ion Cyclization.

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SYNTHESIS OF CYCLOPENTENE-FUSED PYRROLOISOQUINOLINONE DERIVATIVE VIA N-ACYLIMINIUM ION CYCLIZATION

ABSTRACT In this research, a new class of pyrrolo[2,1-a]isoquinolinone derivative 7 was prepared. C-4 Hydroxylated 5-ethoxylactam 1b gave 4,5-epoxylactam 2 in high yield instead of isoquinoline derivative 3b under the N-acyliminium ion cyclization condition. The 4,5-epoxylactam 2 was converted to another N-acyliminium ion precursor 6 through base-promoted epoxide ring opening, silylation, and thermal Diels–Alder reaction with cyclopentadiene in high yield. Finally, compound 6 was cyclized in the presence of TiCl4 to provide cyclopentene-fused pyrroloisoquinoline derivative 7.

ChemInform Abstract: High Pressure and Thermal Diels—Alder Reaction of 2‐Vinyl‐benzo[b]furan and 2‐Vinyl‐benzo[b]thiophene. Synthesis of New Condensed Heterocycles.

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High pressure and thermal Diels–Alder reaction of 2-vinyl-benzo[b]furan and 2-vinyl-benzo[b]thiophene. Synthesis of new condensed heterocycles

A new preparation of 2-vinyl-benzo[ b ]furan and 2-vinyl-benzo[ b ]thiophene is described. Diels–Alder reactions of these dienes with 3-nitro-2-cyclohexen-1-one and 2-inden-1-one was examined under thermal and high pressure conditions. The reaction products have been converted to multi-ring heteroaromatic compounds. Graphic

Facile, Completely Regioselective 1,4-Hydrogenations of C60-Diaryltetrazine Monoadducts

Thermal Diels-Alder reactions between C(60) and electron-deficient 3, 6-diaryl-1,2,4,5-tetrazines yield monoadducts possessing a diaryldihydropyridazine function nested atop the fullerene. The diaryldihydropyridazine functions direct a completely regioselective 1,4-hydrogenation, resulting in a racemic mixture of bifunctional bisadduct (+/-)-3.

Stepwise Bond Formation in Photochemical and Thermal Diels−Alder Reactions of C60with Danishefsky's Dienes

Mechanisms of both the photochemical and thermal Diels−Alder reactions of C60 with Danishefsky's dienes are studied on the basis of product stereochemistry, kinetics, and the detection of radical intermediates. A stereochemically defined (1E,3Z)-1-methoxy-2-methyl-3-[(trimethylsilyl)oxy]-penta-1,3-diene (1a) is used as a stereochemical probe in the Diels−Alder reactions with C60. The major Diels−Alder product is trans-adduct (3) rather than cis-adduct (4) in both the photochemical and thermal Diels−Alder reactions. Such stereochemistry indicates that the Diels−Alder reactions proceed by a stepwise mechanism rather than a concerted mechanism. The transient spectra of C60•- formed in photoinduced electron transfer from 1a to the triplet excited state of C60 (3C60*) have been detected successfully in laser flash photolysis of the 1a-C60 system. The observed rate constants determined from the dependence of the quantum yields on the concentrations of Danishefsky's dienes agree well with those for the photoindu...

Studies on the Synthesis of Natural Products with Bicyclo[4.4.0]decene Skeleton: Synthesis and Uncatalysed Intramolecular Diels–Alder Reactions of the Decatrienone Substrates

Starting from enones 7 and 8 siloxydienes 9 and 12 were synthesized. Cyclopropanation and subsequent alkylation with sorbyl bromide provided tetrasubstituted siloxycyclopropanes 15 and 16 in good overall efficiency. Their ring cleavage with fluoride reagents gave 1,7,9-decatrienones 5 and 17; the latter was converted into the protected compound 6. The thermal intramolecular Diels–Alder reactions of 5 and 6 were compared with those of related trienones 3 and 4. Octalones 1, 2, 21, and 22 were formed as mixtures of three or four diastereomers. Thus, for the stereoselective construction of natural products such as α-eudesmol or dihydromevinolin alternative reaction conditions for the cycloaddition step have to be developed.

Anomalous Products from the Thermal Diels−Alder Reaction of a (E)-2-Thiophenyl Butadiene Tethered to 3-Methallyl Cyclohexenone

Anomalous Products from the Thermal Diels−Alder Reaction of a (<i>E</i>)-2-Thiophenyl Butadiene Tethered to 3-Methallyl Cyclohexenone

One-Step Synthesis and Highly Regio- and Stereoselective Diels−Alder Cycloadditions of Novel exo-2-Oxazolidinone Dienes

An improved synthesis of exo-heterocyclic dienes like N-substituted 4,5-dimethylene 2-oxazolidinones 1, by a one-step method from diacetyl and isocyanates, was described. This highly convergent synthetic strategy has been successfully used for the preparation of novel (Z)-5-ethylidene-4-methylene analogs 4 in fair yields. Both dienes 1 and 4 undergo efficient addition of symmetric dienophiles in thermal Diels−Alder reactions, inasmuch as they react stereo- and regioselectively with the unsymmetric olefins methyl vinyl ketone (MVK) and methyl propiolate. This regioselectivity was greatly improved by using Lewis acid catalysts (TiCl4, AlCl3). The nitrogen atom of the 2-oxazolidinone ring seems to control the orientation of the dienophile approach. These results have been rationalized in terms of the frontier molecular orbital theory by ab initio calculations. For dienes 4, addition of MVK gave the endo isomer as the major product. Dimerization of dienes 4 was also highly regio-, chemo-, and stereoselective, giving only isomer 17. This reaction furnished a second product, which corresponded to dienes 18 obtained by the [1,5] sigmatropic rearrangement of 4. The structure of the dienes and main products was established by NMR experiments and X-ray diffraction analysis.

Hexachlorocyclopentadiene in diels—alder asymmetric reaction

Asymmetric thermal Diels—Alder reactions with chiral dienophiles l-menthyl acrylate and l-menthyl allyl ether, using hexachlorocyclopentadiene (HCC) gave cycloadducts of up to 150%ee. Milder reaction conditions achieved by the use of Lewis acid catalysis increased the optical yields up to 2.8 fold. The catalyzed and uncatalyzed reactions using l-menthyl acrylate result in the formation of adducts having opposite configurations. The products have also been resolved via diastereomer formation as pure enantiomers.

Synthesis and physicochemical properties of bolaamphiphiles from dimeric acid

The physicochemical behaviour of bolaamphiphile derivatives with an anionic, a cationic, or a non-ionic polar group and their mixtures is studied mainly by surface tension measurements, quasi-elastic light-scattering studies, 1H NMR spectroscopy, and surface monolayers. Bolaamphiphiles are synthesized by classical methods from a non-expensive mixture of α,ω-dicarboxylic acids, obtained by thermal Diels–Alder type cyclization of methyl 10-E,12-E linoleate, obtained from tall oil. The anionic and cationic bolaamphiphiles synthesized are water soluble and form stable monolayers when they are compressed. The anionic and the cationic bolaamphiphiles with an iodide atom as counter-anion show a behaviour between liquid-condensed and liquid-expanded. The other synthesized cationic bolaamphiphiles and the (1:1) mixtures of anionic–cationic bolaamphiphiles behave as liquid-condensed.