Search results

Search for "diradical" in Full Text gives 34 result(s) in Beilstein Journal of Organic Chemistry.

Polar reactions of acyclic conjugated bisallenes

  • Reiner Stamm and
  • Henning Hopf

Beilstein J. Org. Chem. 2013, 9, 36–48, doi:10.3762/bjoc.9.5

Graphical Abstract
  • previously by Pasto [26]. In the first step, oxygen attacks the substrate under formation of the diradical 42. This, in turn, closes from its resonance structure 43 to yield the isolated product 44. Had the oxidation taken place at the unsubstituted allene moiety of 3, the tert-butyl substituent would have
PDF
Album
Supp Info
Full Research Paper
Published 08 Jan 2013

The chemistry of bisallenes

  • Henning Hopf and
  • Georgios Markopoulos

Beilstein J. Org. Chem. 2012, 8, 1936–1998, doi:10.3762/bjoc.8.225

Graphical Abstract
  • -shift to provide the diradical intermediate 90. In the next step the ring is split to furnish derivative 91, which, by another TMS-shift, isomerizes to the propargylallene 92. The sequence ends with still another TMS-relocation to provide the final product 88. Both, 91 and 92 are pyrolysis products
PDF
Album
Review
Published 15 Nov 2012

Photoreactions of cyclic sulfite esters: Evidence for diradical intermediates

  • Rick C. White,
  • Benny E. Arney Jr. and
  • Heiko Ihmels

Beilstein J. Org. Chem. 2012, 8, 1208–1212, doi:10.3762/bjoc.8.134

Graphical Abstract
  • cyclic carbonates 1a and 1b (Scheme 1) generate products derived from 1,3-diradical intermediates [14]. Interestingly, the photoinduced fragmentation reactions of nitrogen- and oxygen-containing functionalities have been studied intensively, whereas reports on photoextrusion reactions of sulfur
  • glycol sulfite (8) and the hydrobenzoin sulfite (9); and we herein demonstrate that diradical intermediates are generated during the photoextrusion processes. Results and Discussion Styrene glycol sulfite 8 was prepared from thionyl chloride and styrene glycol in the presence of triethylamine [19]. The
  • decarbonylation results in an alkyl radical. The latter reaction yields bibenzyl (4) and toluene (7) in the photoreaction of 8. It should be noted that the diradical BR2 may be formed also upon photoinduced ring-opening reaction of an intermediate oxirane 2a, which is not detectable in the reaction mixture
PDF
Album
Supp Info
Full Research Paper
Published 30 Jul 2012

Valence isomerization of cyclohepta-1,3,5-triene and its heteroelement analogues

  • Helen Jansen,
  • J. Chris Slootweg and
  • Koop Lammertsma

Beilstein J. Org. Chem. 2011, 7, 1713–1721, doi:10.3762/bjoc.7.201

Graphical Abstract
  • -triene [14]. Besides the 1–2 interconversion, the C7H8 system is rich in rearrangements (Scheme 3). In 1957, Woods found that bicyclo[2.2.1]hepta-2,5-diene (12) converts to cycloheptatriene (1), which was postulated to proceed via diradical 11 and norcaradiene (2) [28]. Instead, pyrolysis of 1 yielded
  • toluene, presumably through a [1,3]-H shift of the diradical [29]. Norcaradiene (2) can also undergo a [1,5]-carbon circumambulatory rearrangement (“walk”), as was discovered by Berson and Willcott in 1965 [30][31]. Although, this process should proceed with retention of the configuration according to the
PDF
Album
Review
Published 21 Dec 2011

Fine-tuning alkyne cycloadditions: Insights into photochemistry responsible for the double-strand DNA cleavage via structural perturbations in diaryl alkyne conjugates

  • Wang-Yong Yang,
  • Samantha A. Marrone,
  • Nalisha Minors,
  • Diego A. R. Zorio and
  • Igor V. Alabugin

Beilstein J. Org. Chem. 2011, 7, 813–823, doi:10.3762/bjoc.7.93

Graphical Abstract
  • ]. The mechanism of triplet photocycloaddition involves a sequence of radical closures initiated by the formation of a triplet 1,4-diradical via the reaction of 1,4-CHD and the alkyne π,π*-triplet state. Although several plausible mechanistic pathways converge at the same homoquadricyclane product in
  • upon the addition of a drop of water suggest that benzoxazines are also the intermediate products in our case but are rapidly hydrolyzed during work-up and purification. Although one can suggest the intermediacy of the triplet diradical in the photocyclization of o-amido acetylene 6, this
PDF
Album
Supp Info
Full Research Paper
Published 16 Jun 2011

Intraannular photoreactions in pseudo-geminally substituted [2.2]paracyclophanes

  • Henning Hopf,
  • Vitaly Raev and
  • Peter G. Jones

Beilstein J. Org. Chem. 2011, 7, 658–667, doi:10.3762/bjoc.7.78

Graphical Abstract
  • -diastereomer. If this process took place, it would involve the diradical 20, which could isomerize to 21 with release of strain. The process could also occur a second time to provide a pseudo-geminally substituted [2.2]paracyclophane, now carrying two cyclopentenyl substituents. Should these ring-enlarged
  • paracyclophanes not be observed, this would not necessarily constitute a proof against diradical(oid) intermediates in these reactions. However, if derivatives such as 21 were among the photoproducts the involvement of radicals in the photoisomerizations would be indicated. We therefore reacted the bis-aldehyde 9
  • diradical intermediate of type 17, its lifetime is evidently too short to allow ring-expansion as depicted in Scheme 7. Whether this process might be induced thermally (vinylcyclopropane→cyclopentene rearrangement; [23]) is an open question. Conclusion Although the detailed mechanisms of the
PDF
Album
Full Research Paper
Published 24 May 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

Graphical Abstract
  • shift in the cyclopropanated 1,6-diradical intermediate, which in this case is probably facilitated by the enhanced mobility of the benzylic hydrogen and by the formation of the conjugationally stabilized imine 9 [11]. The 1,3-dipolar cycloaddition/thermal rearrangement domino reaction of BCP (2) with
PDF
Album
Supp Info
Full Research Paper
Published 09 Mar 2011

Heavy atom effects in the Paternò–Büchi reaction of pyrimidine derivatives with 4,4’-disubstituted benzophenones

  • Feng-Feng Kong,
  • Jian-Bo Wang and
  • Qin-Hua Song

Beilstein J. Org. Chem. 2011, 7, 113–118, doi:10.3762/bjoc.7.16

Graphical Abstract
  • 1c) is enthalpy–entropy controlled. A heavy atom effect is suggested to be responsible for these unusual phenomena based on the triplet-diradical mechanism of the Paternò–Büchi reaction. Keywords: benzophenone; heavy atom effect; Paternò–Büchi reaction; regioselectivity; triplet diradical
  • (singlet or triplet or both) on a ground-state olefin. For aromatic carbonyl compounds, the reaction is a triplet cycloaddition, that is, a triplet-excited carbonyl compound adding to an olefin to yield a triplet 1,4-diradical intermediate, which undergoes intersystem crossing (ISC) to produce a singlet
  • 1,4-diradical. Ring-close of the latter gives an oxetane. The higher selectivity observed for the triplet reaction is rationalized by the optional conformation of the intermediate 2-oxabutane-1,4-diyl for ISC to the singlet diradical, which is preferentially controlled by spin-orbit coupling, thus
PDF
Album
Full Research Paper
Published 26 Jan 2011

En route to photoaffinity labeling of the bacterial lectin FimH

  • Thisbe K. Lindhorst,
  • Michaela Märten,
  • Andreas Fuchs and
  • Stefan D. Knight

Beilstein J. Org. Chem. 2010, 6, 810–822, doi:10.3762/bjoc.6.91

Graphical Abstract
  • of the benzophenone 3, on the other hand, delivers a reactive triplet diradical. In addition, in order to combine a photoactive functional group with an affinity label within the same mannoside, the orthogonally protected glycoamino acid scaffold 4 was synthesized and used for the preparation of the
PDF
Album
Full Research Paper
Published 26 Aug 2010
Other Beilstein-Institut Open Science Activities