scholarly journals The mechanism of stereoselectivity in the cycloaddition reactions of α-hydroxy-ortho-quinodimethanes with the fumarate of methyl lactate and mandelate

1993 ◽  
Vol 71 (6) ◽  
pp. 827-833 ◽  
Author(s):  
James L. Charlton ◽  
Shawn Maddaford
Keyword(s):  
Hydrogen Bonding ◽  
Cycloaddition Reaction ◽  
Diels Alder ◽  
Asymmetric Induction ◽  
Cycloaddition Reactions ◽  
Methyl Lactate ◽  
Very High

The Diels–Alder cycloaddition reaction of the fumarate of methyl lactate or methyl mandelate with α-hydroxy-ortho-quinodimethane produces an unexpected exo product with very high asymmetric induction. Experiments and calculations have been carried out that show that the origin of the stereoselectivity in these reactions is related to hydrogen bonding between the α-hydroxy-o-quinodimethane and the lactate or mandelate group in the dienophile.

scholarly journals Enhancing the reactivity of 1,2-diphospholes in cycloaddition reactions

2015 ◽  
Vol 11 ◽  
pp. 169-173 ◽  
Author(s):  
Almaz Zagidullin ◽  
Vasili Miluykov ◽  
Elena Oshchepkova ◽  
Artem Tufatullin ◽  
Olga Kataeva ◽  
...  
Keyword(s):  
Room Temperature ◽  
Cycloaddition Reaction ◽  
Alder Reaction ◽  
Diels Alder ◽  
Alkyl Halides ◽  
Ethyl Iodide ◽  
Para Position ◽  
Cycloaddition Reactions ◽  
Diels Alder Reaction ◽  
Heating Up

Two different approaches have been employed to enhance the reactivity of 1-alkyl-1,2-diphospholes – the introduction of electron-withdrawing groups either at the phosphorus atoms or in the para-position of the arene ring. The alkylation of sodium 1,2-diphospha-3,4,5-triphenylcyclopentadienide with alkyl halides Hal-CH2-R (R = CN, COOEt, OMe, CH2OEt) results in corresponding 1-alkyl-3,4,5-triphenyl-1,2-diphospholes (alkyl = CH2CN (1a), CH2COOEt (1b), CH2OMe (1c), and (CH2)2OEt (1d)), which spontaneously undergo the intermolecular [4 + 2] cycloaddition reactions at room temperature to form the mixture of the cycloadducts, 2a–c, respectively. However the alkylation of sodium 1,2-diphospha-3,4,5-tri(p-fluorophenyl)cyclopentadienide with ethyl iodide leads to stable 1-ethyl-3,4,5-tris(p-fluorophenyl)-1,2-diphosphole (1e), which forms the [4 + 2] cycloadduct 2,3,4,4a,5,6-hexa(p-fluorophenyl)-1-ethyl-1,7,7a-triphospha-4,7-(ethylphosphinidene)indene (2e) only upon heating up to 60 °C. With further heating to 120 °C with N-phenylmaleimide, the cycloadducts 2a–c and 2e undergo the retro-Diels–Alder reaction and form only one product of the [4 + 2] cycloaddition reaction 3a–с, 3e with good yields up to 65%.

Asymmetric induction in Diels–Alder reactions of α-alkoxyorthoquinodimethanes

1989 ◽  
Vol 67 (6) ◽  
pp. 1010-1014 ◽  
Author(s):  
James L. Charlton ◽  
Guy L. Plourde ◽  
Glenn H. Penner
Keyword(s):  
Molecular Orbital ◽  
Geometry Optimization ◽  
Diels Alder ◽  
Asymmetric Induction ◽  
Molecular Orbital Calculations ◽  
Cycloaddition Reactions ◽  
Vinyl Ethers ◽  
The Face ◽  
Face Selectivity ◽  
Alkoxy Groups

It has been shown that dienophiles cycloadd selectively to one face of o-quinodimethanes (o-QDMs) bearing chiral α-alkoxy groups. The face selectivity (diastereoselectivity) increases for the series of chiral groups -OCH(Ph)CH3, -OCH(Ph)CH(CH3)2, and -OCH(Ph)C(CH3)3. A similar effect on the face selectivity of the Diels–Alder reactions of chiral alkoxy vinyl ethers for the same series of chiral groups has been noted previously by others. A mechanism has been proposed to explain the face selectivity in the cycloaddition reactions of the alkoxy o-QDMs. Abinitio molecular orbital calculations with geometry optimization on vinyl 1-phenylethyl ether to determine its lowest energy conformations support the proposed mechanism. The absolute stereochemistries of the o-QDM cycloadducts have been determined to verify the predictions of the model. Keywords: o-quinodimethanes, asymmetric, Diels–Alder, cycloaddition.

Diels–Alder addition of the fumarate and acrylate of S-methyl lactate to α-hydroxy orthoquinodimethanes

1989 ◽  
Vol 67 (4) ◽  
pp. 574-579 ◽  
Author(s):  
James L. Charlton ◽  
Guy L. Plourde ◽  
Kevin Koh ◽  
Anthony S. Secco
Keyword(s):  
Asymmetric Synthesis ◽  
Optical Purity ◽  
Diels Alder ◽  
Asymmetric Induction ◽  
Synthetic Route ◽  
Methyl Lactate ◽  
High Optical Purity ◽  
Single Diastereomer ◽  
Potential Use

The cycloaddition of α-hydroxy orthoquinodimethane, generated photochemically from 2-methylbenzaldehyde, to the fumarate and acrylate of S-methyl lactate has been found to give a single diastereomer with high asymmetric induction (>95% de). This reaction provides a new and versatile synthetic route to substituted tetralins of high optical purity. A trans stereochemistry between the vicinal hydroxyl and carboxylactyl groups has been established for these cycloadducts. This is in contrast to previous work where cis stereochemistry has always been found for major cycloadducts of α-hydroxy o-QDMs. The high asymmetric induction, unusual diastereoselectivity, and the potential use of these reactions in asymmetric synthesis are discussed. Keywords: o-quinodimethanes, Diels–Alder, asymmetric, cycloaddition, induction, diastereoselective.

Asymmetric synthesis of podophyllotoxin analogs

1990 ◽  
Vol 68 (11) ◽  
pp. 2022-2027 ◽  
Author(s):  
James L. Charlton ◽  
Guy L. Plourde ◽  
K. Koh ◽  
Anthony S. Secco
Keyword(s):  
Asymmetric Synthesis ◽  
Natural Product ◽  
Good Yield ◽  
Diels Alder ◽  
Cycloaddition Reactions ◽  
Thermal Generation ◽  
Methyl Lactate ◽  
Model Studies ◽  
Diastereomeric Excess ◽  
Absolute Stereochemistry

Two analogs of podophyllotoxin, with the same absolute stereochemistry as the natural product, have been synthesized from the cycloadduct between α-hydroxy-α′-phenyl-o-quinodimefhane and the fumarate of S-methyl lactate. After initial attempts to produce the cycloadduct from photochemically generated α-hydroxy-α′-phenyl-o-quinodimethane failed, a study of the thermal generation and reaction of α-hydroxy-o-quinodimethane with the fumarate and acrylate of S-methyl lactate was made. A comparison was made of the diastereoselectivity of these cycloaddition reactions to those previously reported, in which the o-quinodimethane was generated photochemically. The α-hydroxy-o-quinodimethane was produced both by the known thermolysis of benzocyclobutenol and by thermolysis of 1-hydroxy-1,3-dihydrobenzo[c]thiophene-2,2-dioxide. The diastereomeric excess for the cycloaddition reactions was found to be greater than 95% with modest (ca. 55%) isolated yields of the major cycloadducts. Following these model studies, it was found that α-hydroxy-α′-phenyl-o-quinodimethane produced thermally from 1-hydroxy-3-phenyl-1,3-dihydrobenzo[c]thiophene-2,2-dioxide could be added to the fumarate of S-methyl lactate with high diastereoselectivity and good yield. The product of this reaction was converted to the podophyllotoxin analogs 7 and 17. Keywords: o-quinodimethanes, asymmetric, Diels–Alder, lactate, podophyllotoxin, lignan.

Intramolecular Diels–Alder and [3+2] Cycloaddition Reactions in the One-Pot Synthesis of Epoxypyrrolo[3,4-g]indazoles

Synthesis ◽  
2019 ◽  
Vol 51 (15) ◽  
pp. 2936-2944 ◽  
Author(s):  
Abdolali Alizadeh ◽  
Kaveh Amir Ashjaee Asalemi ◽  
Mohammadreza Halvagar
Keyword(s):  
Cycloaddition Reaction ◽  
Diels Alder ◽  
Second Step ◽  
Cycloaddition Reactions ◽  
One Pot ◽  
Dialkyl Acetylenedicarboxylate ◽  
One Pot Synthesis ◽  
Three Component Reaction ◽  
Final Compound ◽  
The One

A one-pot approach for the synthesis of epoxypyrrolo[3,4-g]indazoles is presented. The first step was initiated by a three-component reaction of an isocyanide, a dialkyl acetylenedicarboxylate, and 2-furancarboxylic acid, and led to 1,3-dioxoepoxyisoindole, followed by the addition of hydrazonoyl chloride through a [3+2]-cycloaddition reaction in the second step. The key step in the formation of final compound involves a bicyclization strategy through intramolecular Diels–Alder­ (IMDA) reaction.

scholarly journals Catalytic reductive [4 + 1]-cycloadditions of vinylidenes and dienes

Science ◽  
2019 ◽  
Vol 363 (6429) ◽  
pp. 857-862 ◽  
Author(s):  
You-Yun Zhou ◽  
Christopher Uyeda
Keyword(s):  
Diels Alder ◽  
Synthetic Methods ◽  
Asymmetric Induction ◽  
Chiral Ligand ◽  
Cycloaddition Reactions ◽  
Reductive Activation ◽  
Metal Bond ◽  
Metal Metal ◽  
Intramolecular Cycloadditions

Cycloaddition reactions provide direct and convergent routes to cycloalkanes, making them valuable targets for the development of synthetic methods. Whereas six-membered rings are readily accessible from Diels-Alder reactions, cycloadditions that generate five-membered rings are comparatively limited in scope. Here, we report that dinickel complexes catalyze [4 + 1]-cycloaddition reactions of 1,3-dienes. The C1partner is a vinylidene equivalent generated from the reductive activation of a 1,1-dichloroalkene in the presence of stoichiometric zinc. Intermolecular and intramolecular variants of the reaction are described, and high levels of asymmetric induction are achieved in the intramolecular cycloadditions using aC2-symmetric chiral ligand that stabilizes a metal-metal bond.

Polar Diels-Alder Reactions Under Microwave Irradiation Employing Different Heterocyclic Compounds as Electrophiles

2019 ◽  
Vol 16 (6) ◽  
pp. 527-543 ◽  
Author(s):  
Pedro M.E. Mancini ◽  
Carla M. Ormachea ◽  
María N. Kneeteman
Keyword(s):  
Organic Synthesis ◽  
Heterocyclic Compounds ◽  
Ionic Conduction ◽  
Theoretical Calculations ◽  
Cycloaddition Reaction ◽  
Diels Alder ◽  
The Other ◽  
Conventional Heating ◽  
Protic Ionic Liquids ◽  
Solvent Free Conditions

During the last twenty years, our research group has been working with aromatic nitrosubstituted compounds acting as electrophiles in Polar Diels-Alder (P-DA) reactions with different dienes of diverse nucleophilicity. In this type of reaction, after the cycloaddition reaction, the nitrated compounds obtained as the [4+2] cycloadducts suffer cis-extrusion with the loss of nitrous acid and a subsequent aromatization. In this form, the reaction results are irreversible. On the other hand, the microwave-assisted controlled heating become a powerful tool in organic synthesis as it makes the reaction mixture undergo heating by a combination of thermal effects, dipolar polarization and ionic conduction. As the Diels-Alder (D-A) reaction is one of the most important process in organic synthesis, the microwave (MW) irradiation was applied instead of conventional heating, and this resulted in better yields and shorter reaction times. Several substituted heterocyclic compounds were used as electrophiles and different dienes as nucleophiles. Two experimental situations are involved: one in the presence of Protic Ionic Liquids (PILs) as solvent and the other under solvent-free conditions. The analysis is based on experimental data and theoretical calculations.

Synthese neuer Pyridin-C-nukleoside der 2 ,3 -Didesoxyribose durch „inverse“ [4+2]-Cycloaddition Synthesis of Novel Pyridine-C-nucleosides of 2,3-Dideoxyribose by „Inverse“ [4+2]-Cycloaddition

1997 ◽  
Vol 52 (7) ◽  
pp. 851-858 ◽  
Author(s):  
Gunther Seitz ◽  
Johanna Siegl
Keyword(s):  
Cycloaddition Reaction ◽  
Alder Reaction ◽  
Diels Alder ◽  
The Novel ◽  
Protecting Group ◽  
Enol Ethers ◽  
Inverse Electron Demand ◽  
Diels Alder Reaction ◽  
Cyclic Ketene Acetals

The anomeric imido esters 5 and 6, appropriate precursors for C-nucleoside synthesis, were prepared and utilized as heterodienophiles in a Diels-Alder reaction with inverse electron demand to yield the novel, protected 1.2.4-triazine C-nucleosides 8 and 9. They could be deprotected by treatment with 70% trifluoroacetic acid to furnish the free C-nucleosides 10 and 11. The triazine „aglycon“ of 8 contains an electron deficient diazadiene system, highly activated to react with various electron rich dienophiles such as enamines, enol ethers and several cyclic ketene acetals in an „inverse“ [4+2]-cycloaddition reaction. The Diels-Alder adducts spontaneously eliminate N2 and after follow-up reactions the O-TBDPS protected pyridine-C-nucleosides 13, 15, 17,19, 21 and 23 are formed. Removal of the protecting group by treatment with CF3CO2H /H2O leads to the corresponding 2’,3’-dideoxy-β-D-ribofuranosyl- pyridines.

Sign in / Sign up

Export Citation Format

Share Document