Dienophiles In Diels-Alder Reactions Research Articles

Adjustable Regioselectivity for the Diels-Alder Reactions of Sulfolenodipyrrins upon Molecular Engineering on H-Bonds.

The Diels-Alder reactions of sulfolenodipyrrins prove to be an efficient way to construct aromatic ring-fused dipyrrins. However, adjustable annulation is still hard to achieve. To address this, molecular engineering on the H-bond has been employed. The α-position aryl group-modified sulfolenodipyrrins have been synthesized to react with various dienophiles in Diels-Alder reactions, affording the monoannulation products with different regioselectivity in good yields (45-76%). The remaining sulfolenopyrrole in monoadducts can undergo further fusion in the presence of dienophiles and TEMPO, giving the bisadducts with a lactam subunit in an appropriate yield. According to the crystal structures and theoretical calculations, the intramolecular H-bonds between the α-substituent and the nearby pyrrole confine the conjugation pathway of the dipyrrin core. With respect to the normal NH-sulfolenopyrrole, the imino-type one features low aromaticity, from which SO2 extrusion generates more stable dipyrrin-diene, achieving regioselectivity. In addition, aromatic ring fusion results in red-shifted absorption and emission spectra, and the annulation units regulate the emission intensity. This work shows the versatility of intramolecular H-bonds in regulating the reaction through confinement of the conjugation system.

Подходы к эстрогенам на основе аддуктов Дильса-Альдера левоглюкозенона с диеном Дэйн

Levoglucosenone has established itself as a good Michael acceptor and a powerful dienophile in Diels-Alder reactions, dipolar cycloaddition and in a number of other transformations. In the Diels-Alder reactions of levoglucosenone with 1,3-dienes, chiral derivatives of cyclohexene are obtained, which are valuable products for the synthesis of natural compounds. We previously studied the reaction of the interaction of levoglucosenone with Dane diene under catalytic, thermal conditions, at ultrahigh pressures and microwave irradiation. It was found that as a result of the reaction, 2 adducts are formed – (1S,2S,15S,17R)-9-methoxy-18,20-dioxapentacyclo[15.2.1.02,15.0.5,14.06,11]icosa-4,6,8, 10-tetraen-16-one and its isomer, the product of the double bond migration is (1S,2S,14S,15S,17R)-9-methoxy-18,20-dioxapentacyclo[15.2.1.02,15.0.5, 14.06,11]icosa-5(14), 6,8,10-tetraen-16-one. In this work, we have developed methods for the transformation of these Diels-Alder adducts in approaches to compounds with a steroid skeleton. Thus, based on the obtained Diels-Alder adducts, optically active hydrazone was synthesized. An optimal method for deoxygenation of a keto group proceeding by aromatization of cycle B in (1S,2S,14S,15S,17R)-9-methoxy-18,20-dioxapenta-cyclo[15.2.1.02,15.0.5,14.06,11]icosa-5(14),6,8,10-tetraen-16-one, converting it to sulfide, followed by boiling in the presence of Raney nickel. The resulting compound, 9-methoxy-18,20-dioxapentacyclo-[15.2.1.02,15.0.5, 14.06,11]icosa-5(14),6,8,10,12-pentaenone, is a promising synthetic block for use in the synthesis of estrogen – equilenin. The biological activity of the synthesized compounds was predicted using the PASS computer program, which resulted in the identification of derivatives that are promising for the study of antacid, anti-seborrheic, embryotoxic, and anti-cancer properties.

Modulation of Reactivities of Dienophiles for DielsAlder Reactions via Complexation of α,β‐Unsaturated Chelating Amides

AbstractWe describe the modulation of reactivities of dienophiles for DielsAlder reactions via a new principle based on chelating amides positioned adjacent to their CC bond. It is demonstrated for modified acrylic acid derivatives and related dienophiles with three different chelating entities. Complexation of the chelators leads to an intensified electron‐withdrawing effect leading to an enhancement of reactivity in DielsAlder reactions depending on the complexed metal ion. The application of this new approach might be extended to other reactions with reacting entities adjacent to chelating amides.

Lewis acid-catalyzed Diels-Alder reaction of 2-cyclopentenones with Danishefsky’s diene: double bond isomerization of tetrahydro-1H-indene-1,5(7aH)-diones, and attempts on an asymmetric catalysis

This work describes the investigation of the Diels-Alder reaction of the electron-rich diene trans- 1-methoxy-3-trimethylsilyloxy-1,3-butadiene (Danishefskys diene) and the non-activated dienophiles 2-cyclopentenone and 2-methyl-2-cyclopentenone with respect to reactivity, regioselectivity and stereoselectivity. An observed double bond isomerization limits the practicability of 2-cyclopentenone as a dienophile in Diels-Alder reactions. 2-Methyl-2- cylopentenone could be converted quantitatively into one regioisomeric Diels-Alder adduct, however the stereochemical control turned out to be very demanding.

Design and synthesis of tetraazachlorins, tetraazabacteriochlorins and tetraazaisobacteriochlorins

Three approaches to the synthesis of reduced derivatives of tetraazaporphine such as tetraazachlorin, tetraazabacteriochlorin, and tetraazaisobacteriochlorin are reviewed. The first synthesis of alkyl-substituted tetraazachlorins was achieved by the catalytic hydrogenation of magnesium complexes of tetraazaporphines. Two other synthesis approaches for reduced tetraazaporphines based on the mixed condensation of the precursors with different hydrogenation levels and β–β addition reactions have been developed in the last decade. The use of tetramethylsuccinonitrile as the saturated component in the mixed condensation with derivatives of aromatic and heteroaromatic dicarboxylic acids enable the synthesis of oxidation-resistant benzo-; 1,2- and 2,3-naphtho-; pyrazino-; 2,3- and 3,4-pyridino-fused tetraazachlorins, tetraazabacteriochlorins, and tetraazaisobacteriochlorins. Fullerene conjugates of reduced tetraazaporphine derivatives were obtained using 1,2-dicyanofullerene as the source of the hydrogenated sites. Tetraazaporphine can act as dienophile in Diels-Alder reaction with dienes of the anthracene and cyclopentadiene series and also as dipolarophile in 1,3-dipolar cycloadditions with azomethine ylides and nitrones. In addition, the effect of the reduction of peripheral double bonds in tetraazaporphine macrocycle alone, and in combination with annelation of benzene or heterocyclic rings on the absorption spectra is discussed.

Application of 1-(3-Bromo-3,3-difluoroprop-1-ynyl)benzenes in Diels-Alder Reactions: Synthesis ofortho-CF2Br-Substituted Biaryls

1-(3-Bromo-3,3-difluoroprop-1-ynyl)benzenes were found to be good dienophiles in Diels-Alder reactions. Based on this key reaction a new pathway towards biaryls with an ortho-CF2Br group was elaborated.

Novel Use of N-Carboalkoxy α,β-Unsaturated Iminium Ions as Dienophiles in Diels-Alder Reactions

Tricyclic spiro-N,O-acetals have been assembled in a single step by cycloaddition of hydroxymethyl-substituted dienes to iminium ion activated dienophiles that were generated by acidolysis of α,β-unsaturated-N-carboalkoxy-N,O-acetals or β-methoxymethyl-N-carboalkoxy-enamines. The cycloaddition was conducted using Sc(OTf)3 as a mild Lewis acid affording the endo adducts in moderate yields.

Synthesis of new pentafluorosulfanylacrylates (F 5SCH [dbnd]CHCHO, F 5SCH [dbnd]CHCN, F 5SCH [dbnd]CHCOOCH 3) and use of them as dienophiles in Diels-Alder reaction

New pentafluoro-λ 6-sulfanylacrylates (F 5SCH CHCHO, F 5SCH CHCN, F 5SCH CHCOOCH 3) were synthesized by a convenient and efficient method. These compounds are useful as intermediates in the preparation of pentafluoro-λ 6-sulfanyl-containing cyclic and heterocyclic Diels-Alder cycloadducts.

3-Cyclopropyl- and 3-tert-Butyl-Substituted Propyne Iminium Salts as Dienophiles in Diels-Alder Reactions

Starting from cyclopropylacetylene and 3,3-dimethyl-but-1-yne, and an imidoyl chloride 5, the alkynyl imines 6 were prepared and then converted into propyne iminium triflates 7 by N-methylation. These electron-deficient acetylenes were found to be reactive dienophiles in Diels-Alder reactions with cyclopentadiene, furan, 2,3-dimethylbuta-l,3-diene, and anthracene. Reduction of the iminium function, which is present in the cycloaddition products, generates tertiary amines. In this manner, norbornadiene (8, 9), 7-oxanorbornadiene (10, 11), cyclohexa-1,4-diene (12), benzene (13, 14), and dibenzobarrelene (15, 16) derivatives with a novel vicinal substitution pattern were obtained.

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.

Diels—Alder Reaction of 1‐Methyl‐3,6,8‐trinitro‐2‐quinolone.

1-Methyl-3,6,8-trinitro-2-quinolone (1) behaved as the dienophile in Diels-Alder reactions with dienes. When cyclopentadiene was used, cycloadduct 4 was obtained, which was then aromatized on treatment with triethylamine. In the reaction of 1 with hydrazone of 2-butenal, phenanthridine derivative 7 was produced.

Diels‐alder reaction of 1‐methyl‐3,6,8‐trinitro‐2‐quinolone

Abstract1‐Methyl‐3,6,8‐trinitro‐2‐quinolone (1) behaved as the dienophile in Diels‐Alder reactions with dienes. When cyclopentadiene was used, cycloadduct 4 was obtained, which was then aromatized on treatment with triethylamine. In the reaction of 1 with hydrazone of 2‐butenal, phenanthridine derivative 7 was produced.

Reactions of 1-tosyl-3-substituted indoles with conjugated dienes under thermal and/or high-pressure conditions.

The behavior of 1-tosyl-3-acetylindole (1a), N,N-diethyl-1-tosyl-3-indoleglyoxylamide (1b), and 1-tosyl-3-nitroindole (1c) as dienophiles in Diels-Alder reactions under thermal and/or high-pressure conditions was explored with different dienes: isoprene (2), 1-(N-acetyl-N-propylamino)-1,3-butadiene (3), and 1-methoxy-3-trimethylsilyloxy-1,3-butadiene (Danishefsky's diene) (4). Compared to the acylated indoles, the nitro derivative proved to be the best dienophile. In general, the use of Danishefsky's diene led to high-yielding reactions under milder conditions. Likewise, high-pressure conditions proved to be better in producing high yields of products. The advantage of high-pressure over thermal conditions was the ability of the former to generate highly functionalized adducts in better yields, which were otherwise very difficult or impossible to obtain. The use of thermal or high-pressure conditions led to different regio- and/or stereoselectivity in the adducts, allowing control of the regio- or stereoisomer produced.

Synthesis of new tetrapyrrolic derivatives—porphyrins as dienophiles or dipolarophiles

Porphyrins participate as dienophiles in Diels-Alder reactions with ortho-quinodimethanes or pentacene. They can also behave as dipolarophiles in 1,3-dipolar cycloadditions with a range of 1,3-dipoles. These two reaction types were successfully used to synthesize novel chlorins, bacteriochlorins and isobacteriochlorins.

N,N-Diethyl-1-Tosyl-3-Indoleglyoxylamide as a Dienophile in Diels-Alder Reactions. Hyperbaric vs. Thermal Conditions

Under high pressure conditions, the Diels-Alder reaction involving N,N-diethyl-1-tosyl-3-indoleglyoxylamide and 1-(N-acetyl-N-propylamino)-1,3-butadiene produces a highly functionalized intermediate for the synthesis of Indole Alkaloids, in shorter times and higher yields than under thermal conditions.

1-Nitronaphtalene as a Dienophile in Diels-Alder Reactions

the utilization of substitued dienes with electron-donor groups and under high pressure conditions, induces the dienophilic character of 1-nitronaphtalene in Diels-Alder reactions, giving the products with and without the nitro-group, the yield depending on the nature of the dienes substituent groups.

Theoretical investigation on the reactivity of sulfur-centered heterocumulenes as dienophiles in Diels-Alder reactions and endo-lone-pair effect

AM1 and PM3 computations show that thiocarbonyl S-oxide and thiocarbonyl S,S-Dioxide undergo Diels–Alder cycloadditions with cyclopentadiene and anthracene to form thiabicyclic adducts through asynchronous transition structures (TSs) with C(DOUBLE BOND)S π* involving in the reaction at a very early stage. Calculated activation barriers indicate that the dienophilicity of these heterocumulenes decrease gradually with progressive addition of oxygen atom on thiocarbonyl sulfur, in reasonable agreement with experimental observations. Frontier Molecular Orbital (FMO) and deformation energy analyses reveal that the above trend is due to gradual destabilization of lowest unoccupied molecular orbital (LUMO) of the dienophile and increase of deformation energy of both diene and dienophile with increase of oxygen atoms around sulfur. Analysis of bond orders and TS geometries show that the TSs are neither “early” nor “late.” Chlorine substitution on these heterocumulenes does not seem to increase their reactivity contrary to expectations. The reactions of monosubstituted sulfines with cyclopentadiene pass through four very closely lying TSs and stereoselectively form four stereoisomeric products. For the above reason, the computed barriers show a mixed trend although the relative exothermicity of these reactions are in order. © 1998 John Wiley & Sons, Inc. Int J Quant Chem 66: 309–322, 1998

Remote Asymmetric Induction in Lewis Acid-Catalyzed Diels-Alder Reaction of .ALPHA.,.BETA.-Unsaturated Enones Having a Chiral Sulfinyl-Substituted, 5-Membered Aromatic Heterocycle.

Two types of chiral sulfoxides as Diels-Alder dienophiles were synthesized and high levels of diastereoselectivity were observed in cycloadditions. 2-Furyl and 2-thienyl α, β-enones, bearing a chiral sulfinyl group in the heterocycle, served as efficient dienophiles in Diels-Alder reactions, where the catalytic use of aluminium chloride or a lanthanide triflate effected the cycloaddition with cyclopentadiene affording the endo adduct with high diastereoselectivity, ranging from 91% to 98%.

Diels-Alder reactions of a 6-arenyl fulvene with dienes and dienophiles and related chemistry

6-(2-Phenyl ethenyl) fulvene has been shown to participate both as diene and dienophile in Diels-Alder reactions and a facile photochemical transformation of the resulting bicyclo[2.2.2]-octenediones leading to extensively conjugated benzofulvenes has been accomplished.

Diels-Alder-Reaktion eines elektronenarmen C-Acylimins mit Tetraethoxyethylen

The synthesis of two C-acylimines and their reactivity towards electron rich dienophiles inDiels-Alder reactions is described. A [4+2] cycloadduct is obtained only in one case: from the reaction of a C-acylimine substituted by two methoxycarbonyl groups with tetraethoxyethylene. No [2+2] cycloadducts are observed.