Diels-Alder adducts derived from the natural phthalide Z-ligustilide

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.     

Diels-Alder adducts from flavonoid

A quinoflavonoid was synthesized from commercially available products over three steps. The quinoflavonoid turned out to be an excellent dienophile in Diels-Alder reaction. Reactions were easily performed in dichloromethane, and after evaporation of the solvent, expected products were obtained in good yields.     

Structure,conformation and NMR studies on 1,2-dioxane and halogen substituted 1,2-dioxane molecules

Molecular structure and conformational stability of chair and twist conformers of 1,2-dioxane and halogen substituted compounds of the 1,2-dioxane have been studied using ab initio and density functional theory (DFT) methods. The molecular geometries of 1,2-dioxane, 3,6-difluoro, 3,6-dichloro, 3,3,6,6-tetrafluoro and 3,3,6,6-tetrachloro 1,2-dioxane compounds were optimized at HF, MP2, B3LYP and B3PW91 levels of theory by implementing 6-31G* basis set. To study the effect of polar medium, self-consistent reaction field theory is used to optimize the conformers at B3LYP/6-31G* level of theory. The geometrical parameters of chair and twist conformers have been discussed in the light of interaction between lone pair electrons present in the oxygen and substituted halogen atoms. The relative stability of the conformers have been studied using relative energy, maximum hardness principle and thermodynamical quantities. The 13C-NMR chemical shift study for carbon atoms in the title compounds are calculated and the results have been discussed.     

Highly diastereoselective Diels-Alder reactions of Baylis-Hillman adducts

[reaction: see text] Baylis-Hillman adducts were found to be excellent dienophiles in Diels-Alder reactions, providing essentially complete diastereocontrol (although mixtures of endo/exo isomers) with all dienes.     

Restricted rotation involving the tetrahedral carbon—VI : Some Diels-Alder adducts derived from 2-t-butylfuran

1 - t - Butyl - 1,4 - dihydronaphthalene 1,4 - endoxide derivatives were prepared by treating 2 -t- butylfuran with some benzynes to see the effect of the bulkiness on the barrier to rotation. The NMR signals of the t-Bu group of these compounds split at low temperature, showing that the rotation about the C^Bu-C₁ bond was frozen on the NMR time scale. Activation parameters for rotation were obtained by the total line shape analysis. On further lowering of the temperature, the restricted rotation of the Me in t-Bu group was observed. The signals of the Me groups were assigned by taking the chemical shifts and the through-space H-F couplings into consideration.     

Regioselective Diels-Alder cycloadditions and other reactions of 4,5-, 5,6-, and 6,7-indole arynes

The regioselectivity of Diels-Alder cycloadditions of indole arynes (indolynes) at all three benzenoid positions was examined. Cycloadditions with the 4,5-and 5,6-indolynes, derived via metal-halogen exchange from the corresponding o-dibromo indoles, showed essentially no selectivity with 2-t-butylfuran. In contrast, the 6,7-indolyne displayed virtually complete preference for the more sterically congested cycloadduct. This same cycloadduct undergoes a facile acid-catalyzed rearrangement to afford the annulated enone, or alternatively, undergoes hydrolysis and oxidation in the presence of air to give the indolobenzoquinone. The 5,6-difluoroindoles show anomalous behavior and give either 5-fluoro-6,7-indolynes with n-BuLi in ether, or 5,6-indolynes with n-BuLi in toluene. We have also demonstrated that benzenoid indolynes can be easily and conveniently generated by the fluoride-induced decomposition of o-trimethylsilyl triflates.     

Thermally cleavable surfactants based on furan-maleimide Diels-Alder adducts

Two new surfactant molecules are reported that contain thermally labile Diels-Alder adducts connecting the hydrophilic and hydrophobic sections of each molecule. The two surfactants possess identical hydrophobic dodecyl tail segments but have phenol and carboxylic acid hydrophilic headgroups, respectively. Deprotonation with potassium hydroxide affords the formation of water-soluble surfactants. Room temperature aqueous solutions of both surfactants exhibit classical surface-active agent behavior similar to common analagous alkylaryl surfactant molecules. Critical micelle concentrations have been determined for each surfactant through dynamic surface tension and dye solubilization techniques. Small-angle neutron scattering measurements of the aqueous surfactant solutions indicate the presence of spherical micelles with radii of 16.5 angstroms for the carboxylate and 18.8 angstroms for the phenolate. When these surfactants are exposed to elevated temperatures (>50 degrees C), the retro Diels-Alder reaction occurs, yielding hydrophilic and hydrophobic fragments. Aqueous solutions of each surfactant subsequently exhibit a loss of all surface-active behavior and the micellar aggregates are no longer detectable.     

Utility of a chiral 1,3-dioxane template in stereoselective intramolecular Diels-Alder reactions

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.     

Synthesis and Crystal Structure of 1,2-Bis-（p-nitrophenylsulfonamido）-4,5-dinitrobenzene

The title compound, 1,2-bis-(p-nitro-phenylsulfonamido)-4,5-dinitrobenzene, was synthesized and characterized by elemental analysis, IR and 1H NMR. A pale yellow prism crystal of C23H26N8O13S2 (Mr = 686.64) was obtained in DMF solution and determined by single-crystal X-ray diffraction method. It crystallizes in triclinic system, space group P1 with a = 10.346(4), b = 12.210(5), c = 12.976(5) , α = 108.220(8), β = 99.482(4), γ = 95.490(4)°, V = 1516.7(10) 3, Z = 2, Dc = 1.504 g/cm3, F(000) = 712, μ = 0.254, Mr = 686.64, the final R = 0.0561 and wR = 0.1487. One sulfonamido group of the title compound is deprotoned and forms N(3)=C(13). The crystal involves N,N-dimethylamine from the decomposition of DMF and the proton is transferred to N,N- dimethylamine. It is a strong proof for the characterization of deprotoned recognition compound by X-ray single-crystal structure.     

Synthesis of framework olefins using Diels-Alder adducts of fulvene

Conclusions Syntheses are reported for new sterically hindered framework olefins, namely, dimethoxycarbonyl-substituted adamantylidenequadricyclane and trishomocubalidenequadricyclane.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 7, pp. 1700–1701, July, 1989.     

New Diels-Alder type adducts from Morus macroura and their anti-oxidant activities

Fractionation of the ethanolic extract of the stem bark of Morus macroura resulted in the isolation of four new Diels-Alder type adducts, named guangsangons K--N (1, 2, 5, 6), together with two known compounds, mulberrofuran G (3) and K (4). Their structures were determined on the basis of spectroscopic analyses and chemical methods. Furthermore, by means of (1)H-NMR variable temperature experiments and the Cotton curves in the circular dichroism (CD) spectra, the stereochemistry of four new compounds was elucidated. The isolated new compounds showed good activity on anti-oxidant in vitro, with the inhibitory rates of MDA being from 91.8 to 100.0% at concentrations of 10(-5) mol/l.     

Organocatalysis using protonated 1,2-diamino-1,2-diphenylethane for asymmetric Diels-Alder reaction

Bisammonium salts of mono-N-alkylated chiral 1,2-diamino-1,2-diphenylethane (DPEN) were employed in the catalytic and asymmetric Diels-Alder reaction between cyclopentadiene and crotonaldehyde. The N-3-pentyl diamine·2HCl catalyst shows high endo/exo selectivity and endo-enantioselectivity for the cycloaddition, and this organocatalysis is the first example of the use of a chiral 1,2-diamine to generate an imine intermediate which is activated by an internal ammonium Brønsted acid for the cycloaddition in a wet solvent.     

Involvement of organic fluorine substitution in the crystalline packing structures of tricyclic Diels-Alder adducts derived from diarylfulvenes and N-arylimides

Fluorinated tricyclic Diels-Alder adducts derived from corresponding diarylfulvenes and N-arylmaleimides, each of different degree and positions of the fluorine substituents, and including the non-fluorinated parent compound, have been synthesized. Their X-ray crystal structures were determined in order to study the effect of fluorine substitution on the solid state organization in competition with other weak intermolecular interactions. A balanced interplay of C-H?O, C-H?F and especially C-H?π contacts is typical of the crystal packings while other potential interactions such as C-F?F, C-F?π^F, π^H?π^F and Br?Br are secondary or not to be found. Isostructurality calculations and comparison of molecular conformations have been performed in order to structurally classify the compounds depending on the number and mode of fluorination.     

Structural assignment of Diels-Alder adducts: an experimental and theoretical approach

A detailed NMR analysis with total assignment of (1)H and (13)C NMR data for the endo and the exo adducts, obtained by Diels-Alder reaction between 2-cyclohexenone and cyclopentadiene, is described. The unequivocal assignment of the endo and exo structures was performed by (1)H and (13)C NMR. These assignments were supported by theoretical chemical shift calculations at GIAO/HF level using 6-311 + g(2d, p) from optimized structures at the B3LYP/6-31g(d) level.     

Synthesis of Delta(1)-1,2-diazetines via a Diels-Alder cycloaddition approach

[reaction: see text] A novel method for the synthesis of Delta(1)-1,2-diazetines is presented. Diels-Alder cycloaddition of dienophile 4 with five dienes afforded cycloadducts in good to excellent yields. Four of the obtained cycloadducts were converted to the corresponding diazetines.     

Thermally responsive dendrons and dendrimers based on reversible furan-maleimide Diels-Alder adducts

[reaction: see text]. Benzyl aryl ether dendrons and dendrimers containing thermally reversible furan-maleimide Diels-Alder adducts were prepared up to the third generation. The covalent cleavage and reassembly of the dendrons and dendrimers were evaluated by 1H NMR.     

Understanding the Diels-Alder reactivity of 1,2-azaborine analogues

The Diels-Alder reactivity of 1,2-heteroborines (H₄C₄B(H)X, X?=?NH, PH, AsH; O, S, Se) has been computationally explored by means of Density Functional Theory (DFT) calculations. The influence of the HB?=?X fragment on the reactivity of the system has been quantitatively analyzed in detail by means of the so-called Activation Strain Model (ASM) of reactivity. It is found that the interaction between these species and the dienophile is significantly stronger than that computed for their all-carbon isoelectronic counterpart, benzene. In addition, the strain energy plays a key role in the observed reactivity trends. The role of the aromaticity strength of these heteroarenes on the reactivity is also assessed.