ChemInform Abstract: Stereoselective 1,3‐Dipolar Cycloadditions to Heterocyclic Compounds

Fišera, Ľ.; Ondrus, V.; Kubáň, Juraj; Micuch, Peter; Blanarikova, Iva; Jaeger, V.

doi:10.1002/chin.200039256

Cited by 3 publications

(3 citation statements)

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“…More significantly we show that efficient dethreading of [n]semirotaxanes allows isolation of regioselectively pure 1,3-dis-ubstituted triazole compounds. To the best of our knowledge this is the only synthetic method which gives direct access to the 4-regioisomer of 1,3-triazole derivatives without the need for the separation of regioisomers 13,14 and should therefore be an attractive proposition in natural product synthesis.…”

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confidence: 99%

The synthesis of [2], [3] and [4]rotaxanes and semirotaxanes

Tuncel

Steinke

2002

Chem. Commun.

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confidence: 99%

The synthesis of [2], [3] and [4]rotaxanes and semirotaxanes

Tuncel

Steinke

2002

Chem. Commun.

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“…Over the years, nitrones have become important building blocks in organic synthesis. [1][2][3][4][5][6][7][8][9][10] Nucleosides are generally defined as DNA or RNA subunits and consist of both a base moiety such as adenine, thymine, guanine, cytosine and uracil, and a sugar moiety such as D-ribose or 2-deoxy-D-ribose. 11 Many nucleoside analogues have been synthesized with modification of the base, sugar, and phosphate moieties.…”

Section: Introductionmentioning

confidence: 99%

From sugars to modified nucleosides

Hýrošová¹,

Fišera²,

Medvecký³

et al. 2008

Arkivoc

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Two strategies are reported for the diastereoselective synthesis of isoxazolidinyl nucleosides, as potential antiviral agents -a one-step approach based on 1,3-dipolar cycloaddition of sugarderived nitrones with vinyl nucleobases derived from uracil and adenine, as well as a two-step methodology based on the Vorbrüggen nucleosidation of the 5-acetoxyisoxazolidines. The 1,3-dipolar cycloadditions of sugar-derived nitrones with vinyl acetate proceed with very good diastereoselectivity to give the diastereoisomeric isoxazolidines. Condensation of the major diastereomerically pure acetoxyisoxazolidines with silylated uracil, thymine, cytosine, Nacetylguanine and purines occurs with moderate to excellent stereoselectivity with the formation of the expected isoxazolidinyl nucleosides. The stereoselectivity of the addition of the silylated nucleobase is dependent on the structure of the substituent at C-3 originating from the starting chiral nitrone and on the attacking nucleobase.

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“…1,3-Dipolar cycloaddition reactions are versatile organic transformations, used mainly for the synthesis of a variety of five-membered heterocyclic ring systems. − In these reactions, the dipolarophile is normally an alkene/alkyne derivative or a heteroaromatic derivative. In an earlier study, George et al , have shown that bis(phenylazo)stilbene ( 1 ) reacts with acetylenic and olefinic dipolarophiles to give the corresponding 1:1 adducts (Scheme ), arising through a 1,3-dipolar type of cycloaddition.…”

Section: Introductionmentioning

confidence: 99%

Rearrangement of 1,3-Dipolar Cycloadducts Derived from Bis(phenylazo)stilbene: A DFT Level Mechanistic Investigation

2006

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The 1,3-dipolar cycloaddition of bis(phenylazo)stilbene with activated ethene and ethyne derivatives and the subsequent rearrangement of the cycloadducts have been studied using model compounds at the B3LYP/6-31G(d) level of density functional theory (DFT). From the structural and electronic features, a five-membered zwitterionic ring system 9 (1,2,3-triazolium-1-imide system) formed from bis(phenylazo)ethylene is confirmed as the active 1,3-dipole species in the reaction. Formation of the 1,3-dipolar cycloadduct from the alkyne derivative is found to be 26.0 kcal/mol exergonic, and it requires an activation free energy of 19.4 kcal/mol. The 1,3-cycloadduct formed in the reaction undergoes a very facile migration of a nitrogen-bearing fragment, passing through a zwitterionic transition state. A small activation free energy of 8.2 kcal/mol is observed for this step of the reaction, and it is 19.6 kcal/mol exergonic. Further activation of the newly formed rearranged product is possible under elevated temperatures, again passing through a zwitterionic transition state and resulting in the formation of 2,5-dihydro-1,2,3-triazine derivatives. Such derivatives have been recently reported by Butler et al. (J. Org. Chem. 2006, 71, 5679). The charge separation in 9 and the zwitterionic transition states are stabilized through the pi-system of the phenyl rings and the carbonyl groups. Similar structural, electronic, and mechanistic features are obtained for the reaction of 9 with the ethylenic dipolarophile acrylonitrile. Molecular electrostatic potential analyses of the 1,3-dipole and the zwitterionic transitions states are found to be very useful for characterizing their electron delocalization features. The solvation effects can enhance the feasibility of these reactions as they stabilize the zwitterionic transition states to a great extent.

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ChemInform Abstract: Stereoselective 1,3‐Dipolar Cycloadditions to Heterocyclic Compounds

Cited by 3 publications

References 1 publication

The synthesis of [2], [3] and [4]rotaxanes and semirotaxanes

The synthesis of [2], [3] and [4]rotaxanes and semirotaxanes

From sugars to modified nucleosides

Rearrangement of 1,3-Dipolar Cycloadducts Derived from Bis(phenylazo)stilbene: A DFT Level Mechanistic Investigation

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