Cycloaddition Reactions Of Nitrones Research Articles

Theoretical study of 1,3-dipolar cycloadditions of nitrone and fulminic acid with substituted ethylenes

Molecular orbital calculations were performed to examine the electronic effects involved in the regioselectivity in the 1,3-dipolar cycloaddition reaction of nitrone and fulminic acid. The substituted ethylene dipolarophiles were selected to represent a range of electron-donating/withdrawing abilities: amino, methyl, carbaldehyde (both in the s-cis and the s-trans conformations), and nitrile. The reactions were all asynchronous, with early transition sites. The regioselectivity was correlated with the ability of the substituent to donate or withdraw electrons. With electron-donating substituents, the substituent was directed preferentially to the oxygen end of the dipole and this shifted toward the other regioisomer as the electron-withdrawing ability of the substitutent increased. © 1998 John Wiley & Sons, Inc. J Comput Chem 19: 1795–1804, 1998

Straightforward Synthesis of (1-->2)-Linked Pseudo Aza-C-disaccharides by the Novel Cycloaddition of Enantiopure Cyclic Nitrones to Glycals.

The novel, highly stereoselective, intermolecular cycloaddition reaction of enantiopure cyclic nitrones 8 to 1,2-glycals 9 opens the way to a straightforward synthesis of a broad class of new (1-->2)-linked pseudo aza-C-disaccharides 6, suitable substrates for selective inhibition of glycosidase enzymes. The cycloadditions occur with high stereocontrol, displaying preferential interaction between the bottom face of the glycal and the face of the nitrone anti to the substituent on C-3, with the reagents approaching in an exo fashion. The cycloadditions produced tricyclic isoxazolidines 7 that represent nonreducing pseudo aza-C-disaccharides stable to hydrolytic conditions. The target pseudo aza-disaccharides 6 were obtained by sequential deprotection of the hydroxyl groups and isoxazolidine ring-opening.

ChemInform Abstract: Application of Intramolecular Nitrone Cycloaddition Reaction: Synthesis of Chiral Aminocarbocycles and Carbocyclic Nucleosides from Carbohydrate Precursors.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform Abstract: 1,3‐Dipolar Cycloaddition Reactions of Nitrones with Alkyl Vinyl Ethers Catalyzed by Chiral Oxazaborolidines.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Development of the Asymmetric Cycloaddition Reactions and Asymmetric Nucleophilic Addition Reaction Utilizing Tartaric Acid Esters

In order to develop a practical method for the construction of chiral molecules, we have designed a novel chiral system possessing two metal centers utilizing tartaric acid esters : that is, if two reactants are bound to the two metal centers of a dialkoxide derived from tartaric acid ester, they might be ideally oriented and/or activated by the metals and the subsequent reaction can proceed in an enantioselective manner to afford the corresponding optically active products. According to this working hypothesis, we could develop an asymmetric Simmons-Smith reaction, asymmetric 1, 3-dipolar cycloaddition reactions of nitrile oxides and nitrones, and an asymmetric nucleophilic addition reaction of dialkylzincs to nitrones.

ChemInform Abstract: Synthesis of 4‐Alkoxy and 3‐Nitro Substituted Isoxazolidines by Catalyzed 1,3‐Dipolar Cycloaddition Reactions of Nitrones with Vinyl Ethers and Nitro Alkenes.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Application of Intramolecular Nitrone Cycloaddition Reaction: Synthesis of Chiral Aminocarbocycles and Carbocyclic Nucleosides from Carbohydrate Precursors

Application of Intramolecular Nitrone Cycloaddition Reaction: Synthesis of Chiral Aminocarbocycles and Carbocyclic Nucleosides from Carbohydrate Precursors

Lanthanide-catalyzed endo- and enantioselective 1,3-dipolar cycloaddition reactions of nitrones with alkenes

The 1,3-dipolar cycloaddition reaction of alkenes with nitrones was catalyzed by Yb(OTf) 3 or Sc(OTf) 3 giving isoxazolidines in high yields and selectivities. The catalyst Yb(OTf) 3 induce a high endo-selectivity in the reaction of up to 94% de, whereas Sc(OTf) 3 show the highest rate accelerations. Both the conversion and endo-selectivity of the Yb(OTf) 3 and Sc(OTf) 3 catalyzed reactions proved to be dependent on the amount and type of molecular sieves added. The application of different chiral ligands in 1,3-dipolar cycloaddition reactions of a series of alkenes with nitrones catalyzed by Yb(OTf) 3 or Sc(OTf) 3 has been studied and it was found that high endo-selectivities and an ee's of up to 73% could be obtained by the use of Yb(OTf) 3 and 2,6-bis[4(S)-isopropyl-2-oxazolidin-2-yl]pyridine (PyBOX) as the chiral ligand.

New Access to Aza- C-disaccharides by Cycloadditions of Pyrroline N-Oxides to Glycals

A novel, highly stereoselective intermolecular cycloaddition reaction of simple and enantiopure cyclic nitrones to glucose and galactose-derived 1,2-glycals offers a direct access to a new class of pseudoaza-C-disaccharides with isoxazolidine structure, potential glycosidase inhibitors. The synthesis of new (1→2)-linked aza-disaccharides is accomplished by simple reductive ring-opening of the isoxazolidine. © 1997 Elsevier Science Ltd.

ChemInform Abstract: Improvement of TADDOLate‐TiCl2‐Catalyzed 1,3‐Dipolar Nitrone Cycloaddition Reactions by Substitution of the Oxazolidinone Auxiliary of the Alkene with Succinimide.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Microwave Induced 1,3-Depolar Cycloaddition Reactions of Nitrones

1,3-Dipolar cycloaddition reactions involving unreactive nitrones have been carried out successfully under microwave irradiations. The reaction of nitrones 1 and alkene 2 proceeded regiospecifically at atmospheric pressure and the corresponding isoxazolidines 3 were obtained in high yields.

1,3-Dipolar cycloaddition reactions of nitrones with alkyl vinyl ethers catalyzed by chiral oxazaborolidines

The 1,3-dipolar cycloaddition reactions of various Z- and E-nitrones with ethyl vinyl ether and 2,3-dihydrofuran are catalyzed by 20 mol% of chiral oxazaborolidines at room temperature. The effect of high pressure on these reactions is discussed.

An enantioselective route to trans-2,6-disubstituted piperidines

The synthesis of ( S)-2-methyl tetrahydropyridine-N-oxide ( 4), a key intermediate for the enantioselective construction of trans-2,6-disubstituted piperidines via [3+2] nitrone cycloaddition reaction, is described. Nitrone 4 was elaborated to the fire ant venom alkaloid (+)-solenopsin-A ( 2) via intermediate 14.

Synthesis of 2-aza-3-oxatetracyclo [7. 3. 1. 17,11. 02,6]tetradecane derivatives by the 1,3-dipolar cycloaddition reaction of homoadamantane-incorporated nitrones with alkenes

Abstract The 1,3-dipolar cycloaddition reaction of homoadamantane-incorporated nitrones, 4-azahomoadamant-4-ene N -oxide ( 1 ) and 5-methyl-4-azahomoadamant-4-ene N -oxide ( 2 ), with various alkenes afforded 2-aza-3-oxatetracyclo[7.3.1.1 7,11 .0 2,6 ]tetradecane derivatives as the 1:1 cycloadduct. The reaction showed relatively low regio-and stereo-selectivities, however only the 5- endo adduct was not formed. This was rationalized by the steric effect in the course of reaction process on the basis of PM3 calculations of the transition state model.

Improvement of TADDOLate-TiCl(2)-Catalyzed 1,3-Dipolar Nitrone Cycloaddition Reactions by Substitution of the Oxazolidinone Auxiliary of the Alkene with Succinimide.

A significant improvement of metal-catalyzed asymmetric 1,3-dipolar cycloaddition reactions of acyclic nitrones with alpha,beta-unsaturated carbonyl compounds is described using succinimide as a new auxiliary for the alpha,beta-unsaturated carbonyl moiety. In the absence of a catalyst, N-crotonoylsuccinimide reacts with C,N-diphenylnitrone to give the endo-isoxazolidine, whereas in the presence of 10 mol % TiCl(2)(i-PrO)(2) the exo-product is obtained. Four different TiCl(2)-TADDOLate complexes have been tested as catalysts for the 1,3-dipolar cycloaddition reactions, and the most successful catalyst was applied (5 mol %) in a series of reactions between two different alkenoylsuccinimides and three different nitrones. The crude products containing an N-acylsuccinimide moiety were converted directly into the corresponding carboxamides upon treatment with hydrazine. The 1,3-dipolar cycloaddition reactions proceed with a high degree of exo-selectivity, often >90% de, which is an improvement compared with previous experiments performed using the oxazolidinone auxiliary for the alkenoyl moiety. Furthermore, the enantioselectivities are also improved compared with previous work, and ee up to 73% is obtained, which is the highest ee found for these metal-catalyzed exo-selective 1,3-dipolar cycloaddition reactions. The ee can be improved to >90% by recrystallization. The absolute structure of the 1,3-dipolar cycloaddition adduct is determined on the basis of the X-ray crystal structure of a compound with a known configuration. On the basis of this knowledge of the absolute structure of the product the mechanism of the reaction is briefly discussed.

1,3 - Dipolar cycloaddition reactions of 1-aza-1-cyclooctene 1-oxide

The stereochemistry and reactivity of the cycloaddition reactions of eight-membered cyclic nitrone (4) with several alkenes have been studied. The concentrated solution of the cyclic nitrone undergoes polymerization to give acyclic polynitrone (15). The nitrone 4 is found to be less reactive than its seven-membered counterpart. Barrier to nitrogen inversion in one of the cycloaddition product, a 85 fused ring system, was determined to be 55.4 kJ/mol.

ChemInform Abstract: 1,3‐Dipolar Cycloaddition Reactions of Nitrones to Furan‐ and Pyrrole‐ 2,3‐diones and to 4‐Hydroxyquinolin‐2(1H)‐one.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Optically active isoxazolidines via asymmetric cycloaddition reactions of nitrones with alkenes: applications in organic synthesis

Optically active isoxazolidines via asymmetric cycloaddition reactions of nitrones with alkenes: applications in organic synthesis

ChemInform Abstract: Synthesis and Asymmetric (3 + 2) Cycloaddition Reactions of Chiral Nitrones: A Novel System Providing Maximal Facial Bias for Both Nitrone and Dipolarophile.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Synthesis and Asymmetric [3 + 2] Cycloaddition Reactions of Chiral Cyclic Nitrone: A Novel System Providing Maximal Facial Bias for both Nitrone and Dipolarophile

Synthesis and Asymmetric [3 + 2] Cycloaddition Reactions of Chiral Cyclic Nitrone: A Novel System Providing Maximal Facial Bias for both Nitrone and Dipolarophile