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Search for "nitrones" in Full Text gives 31 result(s) in Beilstein Journal of Organic Chemistry.

Carbohydrate-auxiliary assisted preparation of enantiopure 1,2-oxazine derivatives and aminopolyols

  • Marcin Jasiński,
  • Dieter Lentz and
  • Hans-Ulrich Reissig

Beilstein J. Org. Chem. 2012, 8, 662–674, doi:10.3762/bjoc.8.74

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  • diiodide; Introduction During the last few decades carbohydrate-derived nitrones have turned out to be particularly attractive tools for the synthesis of structurally complex compounds [1][2][3][4]. Employed mainly as 1,3-dipoles in cycloadditions [5][6] or as imine analogues in nucleophilic additions [7
  • ][8], these nitrones very often furnish the corresponding products in a highly selective manner. In this context, reactions of lithiated alkoxyallenes with enantiopure nitrones are particularly of interest since they lead by a [3 + 3] cyclisation process to 1,2-oxazine derivatives with excellent
  • ][12]. Although the reactions of lithiated alkoxyallenes, with nitrones bearing substituents with stereogenic centres at the carbon atom, were studied in our group in great detail [13], N-glycosyl-substituted nitrones have so far not been used as electrophiles for this purpose. This type of nitrone has
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Published 30 Apr 2012

Recent developments in gold-catalyzed cycloaddition reactions

  • Fernando López and
  • José L. Mascareñas

Beilstein J. Org. Chem. 2011, 7, 1075–1094, doi:10.3762/bjoc.7.124

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  • ) cycloaddition of related 2-(1-alkynyl)-2-alken-1-ones 10 with nitrones [47]. The reactions provided a very practical entry to bicyclic oxazine derivatives 11, which were obtained in good yields and excellent selectivities (Scheme 5). A plausible mechanism, proposed by the authors, consists of an initial
  • furanyl intermediate featuring an iminium ion (XI). This species undergoes an intramolecular cyclization to yield the observed azepine product, and regenerates the gold catalyst. Very recently, the same group reported a related gold-triggered formal (4 + 3) cycloaddition between nitrones and 1-(1-alkynyl
  • -catalyzed synthesis of polycyclic, fully substituted furans from 1-(1-alkynyl)cyclopropyl ketones [45]. Gold-catalyzed 1,3-dipolar cycloaddition of 2-(1-alkynyl)-2-alken-1-ones with nitrones [47]. Enantioselective 1,3-dipolar cycloaddition of 2-(1-alkynyl)-2-alken-1-ones with nitrones [48]. Gold-catalyzed
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Published 09 Aug 2011

Synthetic applications of gold-catalyzed ring expansions

  • David Garayalde and
  • Cristina Nevado

Beilstein J. Org. Chem. 2011, 7, 767–780, doi:10.3762/bjoc.7.87

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  • ). Nitrones also reacted as dipolarophiles in the presence of AuCl3, even if in some cases copper catalysts were found to be more effective at triggering the corresponding annulations [52]. By contrast, when alkoxy vinyl ethers were employed as dipolarophiles, the cycloaddition takes place prior to the
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Published 07 Jun 2011

Rh-Catalyzed rearrangement of vinylcyclopropane to 1,3-diene units attached to N-heterocycles

  • Franca M. Cordero,
  • Carolina Vurchio,
  • Stefano Cicchi,
  • Armin de Meijere and
  • Alberto Brandi

Beilstein J. Org. Chem. 2011, 7, 298–303, doi:10.3762/bjoc.7.39

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  • Göttingen, Tammannstrasse 2, 37077 Göttingen, Germany 10.3762/bjoc.7.39 Abstract Dienes embedded in quinolizidine and indolizidine structures can be prepared in four steps from cyclic nitrones and bicyclopropylidene. The key intermediates α-spirocyclopropanated N-heterocyclic ketones, generated via a
  • so that the various specific cyclopropane transformations can be used as a synthetic tool. In recent years we have shown that 1,3-dipolar cycloadditions of nitrones 1 to the highly strained alkene bicyclopropylidene (BCP, 2) [5][6][7] afford spirocyclopropanated isoxazolidines 3 [8][9] which, on
  • (Scheme 6). Conclusion Azaheterocycles 14, 15 and 17 containing a spiro-annelated VCP moiety have been synthesized starting from cyclic nitrones and BCP by a three-step two-pot sequence consisting of a 1,3-dipolar cycloaddition, thermal rearrangement and Wittig methylenation. These compounds in the
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Published 09 Mar 2011
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  • -derived nitrones afforded syn- or anti-configured hydroxylamine derivatives 4a–d that were cyclized under Lewis acidic conditions to yield functionalized dihydropyrans cis- or trans-5a–d containing an enol ether moiety. This functional group was employed for a variety of subsequent reactions such as
  • to a tricarboxylic acid core. Keywords: aminopyrans; carbohydrate mimetics; Lewis acids; lithiated enol ethers; nitrones; oxidative cleavage; stereodivergent synthesis; Introduction The pyran structural motif can be found in numerous bioactive natural products. Possible strategies towards their
  • enantiopure aminopyrans E (Scheme 1). The sequence of nucleophilic addition of lithiated enol ethers A to nitrones B and Lewis acid promoted cyclization of the resulting 1,3-dioxolanyl-substituted hydroxylamine derivatives C, delivered the enantiopure dihydropyrans D in a highly stereodivergent fashion [8
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Published 09 Jul 2010

Synthesis of densely functionalized enantiopure indolizidines by ring- closing metathesis (RCM) of hydroxylamines from carbohydrate- derived nitrones

  • Marco Bonanni,
  • Marco Marradi,
  • Francesca Cardona,
  • Stefano Cicchi and
  • Andrea Goti

Beilstein J. Org. Chem. 2007, 3, No. 44, doi:10.1186/1860-5397-3-44

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  • yields from enantiopure hydroxylamines obtained straightforwardly from carbohydrate-derived nitrones. Background Indolizidine alkaloids have widespread occurrence in nature. They can be found in widely different organisms such as bacteria, fungi, higher plants, invertebrates and vertebrates.[1] For
  • . [5][6][7][8][9][10][11][12][13][14][15][16][17][18] We accomplished the total syntheses of some indolizidine alkaloids and of several non-natural analogues employing chiral nitrones as key intermediates, either as dipolarophiles in 1,3-dipolar cycloaddition chemistry [19][20] or as electrophiles in
  • nitrones. Experimental Sections. Experimental procedures, characterization of new compounds. Acknowledgements We thank Cassa di Risparmio di Firenze for granting a 400 MHz spectrometer. Maurizio Passaponti and Brunella Innocenti (Università di Firenze) are acknowledged for technical assistance. We thank
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Published 12 Dec 2007
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