21939-12-8Relevant academic research and scientific papers
Visible-light photoredox-catalyzed synthesis of nitrones: Unexpected rate acceleration by water in the synthesis of isoxazolidines
Hou, Hong,Zhu, Shaoqun,Pan, Fangfang,Rueping, Magnus
, p. 2872 - 2875 (2014)
A new oxidative [3 + 2] cycloaddition of N-substituted hydroxylamines with alkenes was established under visible light photoredox catalysis. This novel protocol provides a rapid, mild, and efficient access to valuable five-membered ring isoxazolidine heterocycles in a concise fashion.
Simultaneous double 1,3-dipolar cycloaddition reactions involving bisnitrones or bisdipolarophiles.1H NMR investigation of the conformational preferences of N-methyl- And N-phenylisoxazolidines
Heancy, Frances
, p. 373 - 378 (2007/10/03)
Bisnitrones la and lb reacted with N-methylmaleimide giving bisisoxazolidines. Diastereospecific reaction of the phenyl substituted dipole la gave 3a whilst the N-methyl dipole lb furnished diastereomeric adducts 3b, 4 and 7 classified as trans,trans, 3b, cis,cis, 4 and cis,trans adducts 7 (major) according to the relative orientation of the 3-H and 4-H protons on each isoxazolidine ring. Similar behaviour was observed in reaction of mono dipoles N-benzylideneaniline N-oxide and N-benzylidenemethylamine N-oxide with phenylenedimaleimide 2. The N-phenyl dipole reacted highly selectively furnishing the trans,trans adduct 8a whilst the N-methyl dipole again gave trans,trans 8b, cis,cis 10 and cis,trans adducts 9 (major). Some of the N-methyl substituted isoxazolidines (3b, 7, 8b, 9b) displayed a number of very broad signals in their rt 1H NMR spectra which sharpened (and duplicated) on cooling. By analogy to the corresponding 1H NMR data of the "hemi-adducts" 5 and 6, and with reference to crystal structure data for 5c [Fig. 1], it was shown that for this group of adducts the 3-H and 4-H protons are trans orientated. The isoxazolidine ring in these adducts equilibrates between the o- and i-conformations [Fig. 2] and at -40°C each conformer can be clearly identified in the 1H NMR spectrum. No line broadening was observed in the 1H NMR spectra of any of the N-phenyl substituted adducts. The conformational freedom of the adducts is thus dictated by the size of the N-isoxazolidine substituent and the relative orientation of the 3-H and 4-H protons. All new cycloadducts reported, 3-10, are prepared as racemic mixtures and stereochemical information portrayed in the drawings implies relative and not absolute relations.
The nature of lithium perchlorate and gallium chloride salt effect in cycloaddition reactions
Shtyrlin, Yury G.,Murzin, Dmitry G.,Luzanova, Natalia A.,Iskhakova, Gulnara G.,Kiselev, Vladimir D.,Konovalov, Alexandr I.
, p. 2631 - 2646 (2007/10/03)
Comparing the acceleration effects of (4 + 2)-, (3 + 2)- and (2 + 2)-cycloaddition reactions in the presence of the salts of two types: gallium chloride in inert solvents and lithium perchlorate (LP) in diethyl ether (DE) it was observed that in the presence of GaCl3 the acceleration effect is approximately the same (104 times) for the studied reactions, while in LPDE medium for the same reactions strong increase (up to 104 times), weak increase or even decrease of the rate and equilibrium constants take place even with the common dienophile depending on the nature of the second reagent. it was suggested that the acceleration effect of cycloaddition reactions in the presence of such Lewis acids as aluminum, gallium or boron halides is due to the sharp increase of Π-acceptor properties of dienophiles and therefore increasing energy of orbital interaction, whereas LPDE medium demonstrates strong stabilization of static and/or dynamic polar forms and favors reactions with charge control.
