Search results for "Cycloaddition"

An Understanding of the Electrophilic/Nucleophilic Behavior of Electro-Deficient 2,3-Disubstituted 1,3-Butadienes in Polar Diels−Alder Reactions. A D…

2008

The electrophilic/nucleophilic behavior of dimethyl 2,3-dimethylenesuccinate 1, an electron-deficient 2,3-disubstituted 1,3-butadiene, in polar Diels-Alder reactions has been studied using DFT methods at the B3LYP/6-31G(d) level of theory. The electronic nature of bonding of the transition structures involved in the cycloaddition reactions of the diene 1 toward the nucleophilically activated dienophile 6 and the strong electrophilically activated dienophile 7 has been carefully examined within the natural bond orbital (NBO) and the topological analysis of the electron localization function (ELF) frameworks. Additionally, a study of the global electrophilicity pattern of the reagents at the …

ChemInform Abstract: Reactions of Pyrano(3,4-b)indol-3-ones with Dienophiles: Consecutive (4 + 2) Cycloaddition/Cycloreversion/1,2 Elimination.

1990

Methylpyrano[3,4-b]indol-3-ones 1 react with selected dienophiles (as acetylene equivalents) in a consecutive Diels-Alder/cycloreversion/1,2 elimination reaction sequence to furnish the 1-methyl- and 1,4-dimethylcarbazoles 4.

Understanding the reactivity of captodative ethylenes in polar cycloaddition reactions. A theoretical study

2008

The electrophilic/nucleophilic character of a series of captodative (CD) ethylenes involved in polar cycloaddition reactions has been studied using DFT methods at the B3LYP/6-31G(d) level of theory. The transition state structures for the electrophilic/nucleophilic interactions of two CD ethylenes toward a nucleophilically activated ethylene, 2-methylene-1,3-dioxolane, and an electrophilically activated ethylene, 1,1-dicyanoethyelene, have been studied, and their electronic structures have been characterized using both NBO and ELF methods. Analysis of the reactivity indexes of the CD ethylenes explains the reactivity of these species. While the electrophilicity of the molecules accounts for…

ChemInform Abstract: Regio- and Stereoselective Synthesis of Spiropyrrolizidines and Piperazines Through Azomethine Ylide Cycloaddition Reaction.

2016

A series of original spiropyrrolizidine derivatives has been prepared by a one-pot three-component [3 + 2] cycloaddition reaction of (E)-3-arylidene-1-phenyl-pyrrolidine-2,5-diones, l-proline, and the cyclic ketones 1H-indole-2,3-dione (isatin), indenoquinoxaline-11-one and acenaphthenequinone. We disclose an unprecedented isomerization of some spiroadducts leading to a new family of spirooxindolepyrrolizidines. Furthermore, these cycloadducts underwent retro-1,3-dipolar cycloaddition yielding unexpected regioisomers. Upon treatment of the dipolarophiles with in situ generated azomethine ylides from l-proline or acenaphthenequinone, formation of spiroadducts and unusual polycyclic fused pip…

Dehydrotriphenylene zum Aufbau gewinkelter molekularer Bandstrukturen

1998

Dehydrotriphenylenes for the Generation of Bent Molecular Ribbons The synthetic sequences 1 11 and 17 23a lead to highly reactive mono- and bisdienophiles whose cycloaddition processes with in situ generated isobenzofuran 13 were studied: 11 + 13 15 and 23a + 2×13 24a.

ChemInform Abstract: Stereoselective Synthesis of Quinolizidine Alkaloids: (-)-Lasubin II.

2008

Initially, lasubin II was synthesized diastereoselectively in racemic form [3]. Asymmetric syntheses of lasubin II were achieved based on stereoselective transformations of enantiomerically pure substrates [4] or, for example, via a diastereoselective aza-Diels-Alder reaction using a resolved chiral arylaldehyde tricarbonylchromium complex [5]. Recently, an enantioselectively catalyzed aza-Diels-Alder reaction [6] and a [2+2+2] cycloaddition reaction [7] were successfully used for the synthesis of enantiomerically pure lasubin II.

Stereoselective Synthesis of Quinolizidine Alkaloids: (–)-Lasubin II

2008

Initially, lasubin II was synthesized diastereoselectively in racemic form [3]. Asymmetric syntheses of lasubin II were achieved based on stereoselective transformations of enantiomerically pure substrates [4] or, for example, via a diastereoselective aza-Diels-Alder reaction using a resolved chiral arylaldehyde tricarbonylchromium complex [5]. Recently, an enantioselectively catalyzed aza-Diels-Alder reaction [6] and a [2+2+2] cycloaddition reaction [7] were successfully used for the synthesis of enantiomerically pure lasubin II.

Book Review: Cycloaddition Reactions in Organic Synthesis. By W. Carruthers

1992

Synthesis and pharmacological activity of silyl isoxazolines 2

2003

Silyl isoxazolines have been synthesized by [2+3] cycloaddition reaction of nitrile oxides to vinyl- and allylsilanes. The addition of 3-pyridylnitrile oxide to 1,3-divinyl-1,1,3,3-tetraphenyldisiloxane affords 1,3-bis{5-[3-(3-pyridyl)isoxazolin-2-yl]}-1,1,3,3-tetraphenyldisiloxane; the latter exists as a mixture of trans- and cis-isomers.The bond angle of the Si–O–Si fragment in thetrans-isomer equals 180(3)° and in the cis-isomer it is 162(3)°.The pharmacological properties of 4-[3-(5-trimethylsilylisoxazolin-2-yl)]pyridinium-chloride have been studied.

DFT Study of the Molecular Mechanism of Lewis Acid Induced [4 + 3] Cycloadditions of 2-Alkylacroleins with Cyclopentadiene

2009

The mechanism of the Lewis acid (AlCl(3)) induced [4 + 3] cycloaddition of 2-methylacrolein with cyclopentadiene (Cp) [ J. Am. Chem. Soc. 2004, 126, 2692] has been examined here through DFT calculations at the MPW1K(DCM)/6-31+G** level. Formation of these seven-membered carbocycles is a domino process that comprises three consecutive reactions. The first one is a polar Diels-Alder reaction that is initialized by the nucleophilic attack of Cp to the beta-conjugated position of acrolein, yielding the formation of the endo and exo [4 + 2] cycloadducts. The corresponding LA-[4 + 2] cycloadduct complexes equilibrate through a skeleton rearrangement with a low free activation energy with two seve…