How important are secondary orbital interactions in favoring the endo mode in 1,3-dipolar cycloadditions of nitrones?

Burdisso, Marina; Gandolfi, Remo; Grünanger, Paolo; Rastelli, Augusto

doi:10.1021/jo00298a001

Cited by 63 publications

(14 citation statements)

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“…1 Purification of the crude oligomer was performed by repeated precipitation of the solution in diethyl ether to yield little amounts of the crude product. The pure reaction products were characterized by IR and NMR spectroscopy, and also by GPC measurements.…”

Section: Resultsmentioning

confidence: 99%

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Novel UV‐Absorbing Nitrones: Synthesis and 1,3‐Dipolar Cycloaddition onto Poly(urethane)s

Bietz

Ritter

2009

Macro Chemistry & Physics

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UV‐absorbing nitrones based on 4‐hydroxybenzophenone and stilbene were synthesized by condensation of derivatives of benzaldehyde with N‐methylhydroxylamine hydrochloride and could be characterized by IR, NMR, UV‐Vis spectroscopy and MS‐EI spectrometry. The ability of the synthesized compounds to undergo 1,3‐dipolar cycloaddition was observed by treatment of an unsaturated, soluble, oligo(urethane) with the new nitrones. The conversion could be determined by IR and NMR spectroscopy and GPC measurements. Additionally the conversion of the nitrones with fumaric acid diethyl ester, as a model compound, could be verified and analyzed by UV and NMR spectroscopy.magnified image

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Section: Resultsmentioning

confidence: 99%

“…Many efforts in organic chemistry [1][2][3][4] and also in polymer chemistry [5][6][7][8] were dedicated to the study of thermal 1,3-dipolar cycloadditions of nitrones. Recently, we described the synthesis of polymers by using bisnitrones and bismaleininimides.…”

Section: Introductionmentioning

confidence: 99%

Novel UV‐Absorbing Nitrones: Synthesis and 1,3‐Dipolar Cycloaddition onto Poly(urethane)s

Bietz

Ritter

2009

Macro Chemistry & Physics

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“…This is in accord with the widely accepted view that approach of the dipole and dipolarophile takes place in two parallel planes 24,25 and that an endo transition state is preferred in the absence of obvious steric interactions. [26][27][28][29]…”

Section: Methodsmentioning

confidence: 99%

Synthesis and Structure of Condensed Heterocycles Derived from Intramolecular 1,3-Dipolar Cycloaddition of Transient and Enantiomerically Pure α-Allylamino Nitrones and Nitrile Oxides in a High Level of Diastereoselectivity

Uddin¹,

Kikuchi²,

Takedatsu³

et al. 2000

Synthesis

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A series of typical nitrone and nitrile oxide derivatives was generated in situ from the corresponding sulfonylated a-allylamino aldehydes and aldoximes, which afforded isoxazolidine and isoxazoline fused heterocycles by intramolecular 1,3-dipolar cycloaddition reactions with a high degree of diastereoselectivity. The structure as well as the absolute stereochemistry of the products were confirmed by extensive 2D-NMR spectroscopy and single crystal X-ray analyses and the reasons for the observed selectivity were explained by the energy calculations of the transition states using semiemprical (MOPAC AM1 and MOPAC PM3) and ab initio methods (3-21G* and 6-31G*).Reactions in which the formation of a new carbon-carbon or carbon-heteroatom bond provide new stereogenic centers with a high level of enantio-and diastereoselectivity are of special interest for asymmetric synthesis. 1 The 1,3-dipolar cycloaddition is such a reaction, which conserves the stereochemistry of the alkene, and in which, a stereocenter on the dipole is often able to influence the relative stereochemistry of the newly formed stereogenic centers in the product. 2 Even greater stereocontrol is possible when both reactants are a part of the same molecule, the intramolecular nature, which often enhances the stereoselectivity of the cyclization process. 3,4 As a result, this type of cyclization could be applied to the synthesis of targeted macromolecules, for example, sugar derivatives, 5 b-lactams, 6 amino acids, 7 alkaloids 8 and other interesting classes of compounds. Also, considerable attention has been paid to a basic survey of this process but the general rules for the regio-and stereoselectivities are still obscure. 9 Among the other 1,3-dipolar cycloadditions, the intramolecular nitrone olefin cycloaddition and intramolecular nitrile oxide olefin cycloaddition have been of considerable synthetic and mechanistic interest, 10,11 especially since the resulting heterocycles can serve as precursors of synthetic equivalents, 12 such as amino alcohols, 13 and hydroxy ketones, 14 or other functional groups. 15 More closely, while isoxazoli(di)nes are very readily available, their potential as latent synthetic equivalents has only recently begun to be realized. 16 On the other hand, the dipolarophilic activity of the C-C double, triple or heteromultiple bonds depends significantly on the belonging substituents and the introduction of electron-donating or electron-withdrawing substituents on the dipole or the alkene can alter the relative frontier orbital energies, [17][18] which could influence the reactivity as well as the selectivity of the process. 19 Recently, we have described a series of chiral auxiliary controlled diastereoselective intramolecular Diels-Alder reactions of sulfonyl-substituted trienes. 20 In this paper, we report a series of intramolecular 1,3-dipolar cycloaddition reaction of nitrones and nitrile oxides with alkenes having an electron-withdrawing substituent and which contain a chiral auxiliary at the allylic position. In additio...

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“…7 There are reports that the dipolar cycloaddition reactions of nitrones (both cyclic and open-chain) with VC lead to the formation of mixtures of endo-and exo-adducts. 8 However, nitrones bearing a chiral center on the carbon substituent of a nitrone undergo endo additions with achiral dipolarophiles. 9 This chemistry leads directly to the formation of masked α-hydroxy aldehydes and presents an attractive route for preparing amino sugars from noncarbohydrate precursors.…”

Section: 3-dipolar Cycloaddition Reactionsmentioning

confidence: 99%

Vinylene Carbonate

Ateeq

Iqbal

2001

Encyclopedia of Reagents for Organic Synthesis

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How important are secondary orbital interactions in favoring the endo mode in 1,3-dipolar cycloadditions of nitrones?

Cited by 63 publications

References 0 publications

Novel UV‐Absorbing Nitrones: Synthesis and 1,3‐Dipolar Cycloaddition onto Poly(urethane)s

Novel UV‐Absorbing Nitrones: Synthesis and 1,3‐Dipolar Cycloaddition onto Poly(urethane)s

Synthesis and Structure of Condensed Heterocycles Derived from Intramolecular 1,3-Dipolar Cycloaddition of Transient and Enantiomerically Pure α-Allylamino Nitrones and Nitrile Oxides in a High Level of Diastereoselectivity

Vinylene Carbonate

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