Intramolecular diels-alder reaction with furan-diene. An expeditious entry into a functionalized gibbane.

A short synthesis of a functionalized gibbane is described. The key-step involves the intramolecular Diels-Alder reaction of furan-diene $\text{12}$, leading to a 3:1 ration of two diastereoisomers, tentatively identified as $\text{14a}$ and $\text{14b}$. The precursor $\text{12}$ is obtained form-m-methoxybenzoic acid in 7 steps.     

Intramolecular diels-alder reaction with furan-diene. A novel potential entry to steroids.

Depending on the reaction conditions the intramolecular Diels-Alder reaction of furan-diene $\text{14}$ yields predominantly either one of two adducts $\text{16a}$ and $\text{16b}$, which possess the necessary functionality for eventual transformation into corticosteroids. The dienophile was introduced via alkylation of the enolate, formally obtained upon lithium-liq. ammonia reduction of 3-furyl-2-methyl-2-cyclopentenone ($\text{7}$).     

Intramolecular diels-alder reaction with furan-diene: Total synthesis of (±)-11-ketotestosterone and (±)-adrenosterone

A novel D → BCD → ABCD route to 11 -keto steroids is reported involving a high yield stereoselective intramolecular Diels-Alder reaction of furan-diene $\text{12}$ in water as a key-step. The dienophilic side chain is readily introduced starting from $\text{8}$ via a sequence involving alkylation with ethyl ($\text{E}$)-3-ethoxy-4-iodo-2-butenoate, reduction and acid hydrolysis. The reduced adduct $\text{14}$ is further converted into (±)-adrenosterone ($\text{6}$) via $\text{24}$, the dienediolate equivalent of which is a known intermediate in corticosteroid synthesis.     

Intramolecular diels-alder reactions of dienamines with acrylates: trends in stereoselectivity upon substitution.

Intramolecular Diels-Alder reactions of all-$\text{trans}$ ethyl 10-diethylamino-2,7,9-decatrienoate and 11-diethylamino-2,8,10-trienoate occur readily to produce $\text{trans}$ and $\text{cis}$-fused products in ratios of 85:15 and 55:45, respectively.     

Intramolecular diels-alder reaction by self-assembly of the components on a lewis acid template

Diels-Alder reactions of 2,4-hexadienol or its O-methyl ether with acrylate derivatives at 120 degrees C give mixtures of the four possible adducts with low selectivity. At ambient temperature and in the presence of Mg(II) or Al(III) Lewis acids, reactions of the dienol (but not the ether) are highly selective. Control experiments suggest that the Lewis acid serves both to tether the diene and dienophile and to induce an "intramolecular" reaction of the resulting "self-assembled" intermediate.     

Intramolecular diels-alder reaction of bicyclo[6.4.0] dodeca-4,9,11-triene

cis-Bicyclo[6.4.0]dodeca-4,9,11-triene (5) has been synthesized and the kinetics of its intramolecular Diels-Alder reaction have been measured from 50–75°C     

Diels-Alder reaction of sugar-derived cyclic dienophiles with cyclopentadiene. Factors affecting the reactivity and stereoselectivity

[formula: see text] A sugar-derived cyclic dienophile showed a high exo and face selectivity in the Diels-Alder reaction with cyclopentadiene. Structural modifications on the dienophile structure were made, and the outcomes of the cycloaddition reactions were investigated. These results and the spectroscopic data recorded within a series of analogues were used to analyze the factors affecting the reactivity and exo selectivity.     

Intramolecular diels-alder reactions. IX. Syntheses of N-benzylcyclolignan lactams

Four bis-unsaturated N-benzyl amides of the type where (C₂) and (C₂)' are variously trans-CH?CH and C?C groups, were synthesized and refluxed in acetic anhydride. Three of them cyclized to form N-benzylcyclolignan lactams by intramolecular Diels-Alder processes. In one case [(C₂) ? C?C, (C₂)' ? trans-CH?CH] the (C₂) unit functioned as the dienophilic moiety.     

Predicting reactivity and stereoselectivity in the Nazarov reaction: a combined computational and experimental study

The Nazarov reaction of pentadienyl cations generated by protonation of either dienones or alkoxytrienes has been examined in detail both experimentally and by DFT calculations. In particular, calculations at the B3LYP/6‐311G** level of theory accurately predicted, and accounted for, the outcome of the Brønsted acid catalyzed electrocyclization of 4π‐electron systems in which one of the double bonds involved in the process was embedded in N‐ and S‐heterocyclic rings. Calculations showed that both heteroatoms are capable of accelerating the ring closure by stabilizing the partial positive charge which develops at C‐6 (C‐2) in the transition state, with S‐heterocyclic derivatives being more reactive than the corresponding N‐containing compounds. In general, pentadienyl cations generated by protonation of alkoxytrienes were expected to react faster than those obtained by protonation of the corresponding dienones, as the latter were stabilized by a hydrogen bond. The presence of a substituent on the heterocyclic ring significantly affects the stereoselectivity (torquoselectivity) only in the case of the N‐heterocyclic derivatives, in which a 2‐alkyl group is axially oriented, providing the cis‐2,5‐disubstituted isomer only. Instead, with substituted S‐heterocyclic compounds, the anticipated torquoselectivity was very low and, in fact, a 3:1 diastereomeric mixture between the trans and cis products was experimentally found after ring closure. For this study, the synthesis of the appropriate N‐ and S‐containing dienones and alkoxytrienes was realized to evaluate the predictivity power of the DFT computations, which was very good in all of the cases examined, both in terms of reactivity and stereoselectivity. The consistency observed between computational and experimental results, therefore, shows the usefulness of DFT calculations at the B3LYP/6‐311G** level of theory as a robust instrument for the prediction of reactivity and stereoselectivity in the Nazarov electrocyclic reaction.     

Intramolecular diels-alder reactions of 1,3,8-nonatriene and 1,3,9-decatriene

The stereoselectivities of the title reactions have been investigated from 140–340°C, and relative activation parameters for $\text{cis}$ and $\text{trans}$ product formation have been determined.     

An efficient route to aminoanthraquinones and derivatives via a diels-alder reaction.

Cycloadditions of (E)-1-N-carbobenzoxyamino-1,3-butadiene to naphtoquinones followed by aromatization of the adducts and deprotection of the amino group afford regioselective syntheses of −5 and −8 substituted aminoanthraquinones.     

Intramolecular diels-alder cycloadditions of vinylketenimines. A convergent route to carbazoles and pyridocarbazole alkaloids

The intramolecular Diels-Alder cycloaddition of acetylenic vinylketenimines is the key step of a highly convergent synthesis of carbazoles. A facile synthesis of N-methyl-tetrahydroellipticine has been completed in five isolated steps from N-methyl piperidone.     

Intramolecular diels-alder reactions of diester-tethered trienes. synthesis of medium ring-containing carbocycles and heterocycles

Intramolecular Diels-Alder reactions of cyclohexane-1,2-dicarboxylic anhydride-derived diester-tethered trienes are described. The stereoselectivities of most of the cycloaddition processes studied may be rationalised in terms of an preferred ‘inside’-oriented diene giving rise to an endo-transition state.     

Synthesis of phenylated phthalimides. The diels-alder reaction of tetraphenylcyclopentadienone with maleimides

A series of phenylated dihydrophthalimides has been synthesized by the Diels-Alder reaction of tetraphenylcyclopentadienone with maleimide, N-phenylmaleimide, and N,N'-o-, -m-, and -p-phenylenedimaleimide. Subsequent dehydrogenation of these compounds yielded the corresponding phenylated phthalimides. These phthalimides were also obtained in one step when the initial reactions were carried out in refluxing nitrobenzene.     

1,2,4-triazines in organic synthesis. 8. Intramolecular diels-alder reaction of 5-acyl-1,2,4-triazineoxime ethers. New route of synthesis of alkylhetarylketones

Intramolecular diene cycloaddition of 5-acyl-1,2,4-triazineoxime ethers involving a dienophile substituent in the 3-position of the triazine ring is studied. New alkylhetarylketones are synthesized by hydrolysis of the condensed N- and O-containing heterocyclic products. The starting materials are prepared by oxidation of 5-acetyl- and 5-butyryl-3-methylthio-1,2,4-triazineoxime ethers with KMnO₄ to the sulfonyl derviatives with subsequent replacement of the CH₃SO₂ group by sodium 3-butyn-1-oxide, 4-pentyn-1-oxide and o-cyanophenoxide.For Communication 7, see [1].Institute of Chemistry, Agricultural and Teachers University, Siedlce, 08–110, Poland.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 381–389, March, 1999.     

An experimental and theoretical study of stereoselectivity of furan-maleic anhydride and furan-maleimide diels-alder reactions

The stereoselectivity of the reaction of furan (1) with maleic anhydride (2) and maleimide (3) was studied experimentally and theoretically. Although the two reactions are highly similar with regard to their preference for endo and exo steroisomers, notable differences were experimentally observed and explained on the basis of calculated reaction-free energies and transition-state barriers. The experimental values of rate constants (k(1+2endo) = (1.75 +/- 0.48) x 10(-5); mol(-1) l s(-1); k(1+2exo) = (3.10 +/- 0.55) x 10(-5); mol(-1) l s(-1); k(1+3endo) = (1.93 +/- 0.082) x 10(-5); mol(-1) l s(-1), k(1+3exo) = (1.38 +/- 0.055) x 10(-5); mol(-1) l s(-1) all at 300 K) and the observed reaction course clearly confirm that neither of these reactions are prototypical examples of Diels-Alder [4 + 2] cycloadditions, whose dominant preference is for endo isomers. However, only by comparing their energetics-calculated at the CCSD(T) level of theory-with the analogous reactions involving cyclopentadiene (8) as a diene can these observations be understood. The low thermodynamic stability of furan [4 + 2] adducts opens retro-Diels-Alder reaction channels and overrules the very small kinetic preference (calculated and measured here) of initial formation for endo stereoisomers. On a macroscopic scale "an irregular"-thermodynamically more stable-exo stereoisomer was consequently observed as a dominant species.     

A practical and general diels-alder reaction of pentafulvenes with arynes

A high-yielding, versatile and practical Diels-Alder reaction of pentafulvenes with arynes under mild reaction conditions is reported. The aryne generated by the fluoride induced 1,2-elimination of 2-(trimethylsilyl)aryl triflates undergoes efficient cycloaddition with 6-substituted and 6,6-disubstituted pentafulvenes leading to the formation of benzonorbornadiene derivatives.     

The effect of a centrifugal field on a diels-alder reaction

Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 9, p. 2151, September, 1989.     

Intramolecular diels-alder reactions. XI. Modal selectivity in the syntheses of some parent cyclolignan lactones

Ph(C₂)CH₂Cl and Ph(C₂)'CO₂Na [where (C₂) = -C=C- or trans-CH=CH-, (C₂)' = -C=C- or cis-CH=CH-] reacted in refluxing dimethylformamide to yield unsaturated esters Ph(C₂)'CO₂-CH₂(C₂)Ph and/or their intramolecular Diels-Alder cyclization products (cyclolignan lactones). It was found that modal selectivity for cyclization in DMF sometimes varies from that found previously with acetic anhydride as solvent. Two new parent tetrahydrocyclolignan lactones were synthesized.