Cycloaddition reactions of activated exo-glycals and nitrones proceeded only under microwave activation, with excellent facial selectivities on furanoglycosylidenes and good stereocontrol on the nitrone producing only two diastereomeric spiroisoxazolidines. alpha/beta-Spiro sugar-isoxazolidines are obtained from pyrano exo-glycals. The cycloaddition reaction with nitrile oxide proceeds at room temperature and gives open-chain isoxazoles due to facile beta-elimination of the sugar ring oxygen on the intermediate isoxazoline ring system. All the heterocycles obtained this way can be regarded as nucleoside analogues. (C) 2005 Elsevier Ltd. All rights reserved.
作者:Bruce H. Toder、George B. Mullen、Vassil St. Georgiev
DOI:10.1002/hlca.19900730119
日期:1990.1.31
Adamantanone-derived nitrone 4 and some other keto-nitrones, when reacted with aromatic and aliphatic aldehydes in refluxing toluene or tetrahydrofuran, formed the corresponding aldonitrones (Z)-10, the latter arising from the fragmentation of an initially formed 1,4,2-dioxazolidine 6 to adamantan-2-one and an oxaziridine intermediate 11, which then rearranges to (Z)-10.
Lipase-catalyzed asymmetric synthesis of oxathiazinanones through dynamic covalent kinetic resolution
作者:Lei Hu、Yan Zhang、Olof Ramström
DOI:10.1039/c4ob00365a
日期:——
A domino addition–lactonization pathway has been applied to a dynamic covalent resolution protocol, leading to efficient oxathiazinanone formation as well as chiral discrimination. A new, double biocatalytic pathway has furthermore been proposed and evaluated where the initial product inhibition could be efficiently circumvented.
Organocatalysts Promote Enantioselective 1,3-Dipolar Cycloadditions of Nitrones with 1-Cycloalkene-1-carboxaldehydes
作者:Staffan Karlsson、Hans-Erik Högberg
DOI:10.1002/ejoc.200300172
日期:2003.8
In the presence of enantiopure organocatalysts, 1-cycloalkene-1-carboxaldehydes and various nitrones furnished fused isoxazolidines. Thus, some chiral pyrrolidinium salts catalyzed the formation of such cycloadducts in high diastereo- and enantioselectivity (up to 92% ee). The predominant diastereomer, the exo one, was mostly obtained in excellent diastereoselectivity (> 99:1 dr). Furthermore, after
A new, stereoselective approach to pyrrolidine-N-oxides by sequential condensation of sulfones with nitrones and reverse-cope elimination
作者:Andrew R. Wheildon、David W. Knight、Mathew P. Leese
DOI:10.1016/s0040-4039(97)10245-3
日期:1997.12
Lithiosulfones 10 condense smoothly and highly stereoselectively with nitrones 11 to give unsaturated hydroxylamines 12 which undergo reverse-Cope cyclisations at varying rates leading to pyrrolidine-N-oxidies 13 and 14; the former isomerized slowly to diastereoisomers 20. (C) 1997 Elsevier Science Ltd.
Solvent-free synthesis of nitrones in a ball-mill
作者:Evelina Colacino、Pierrick Nun、Francesco Maria Colacino、Jean Martinez、Frédéric Lamaty
DOI:10.1016/j.tet.2008.03.091
日期:2008.6
13C MAS nuclear magnetic resonance experiments. We have also studied the temperature profile during the reaction. A comparative study with the corresponding solvent-free microwave activated reaction showed the superiority of the ball-milling method; 31 examples are described, including the synthesis of the anti-aging agent C-phenyl-N-tert-butyl nitrone (PBN) and one of its analogues C-2-pyridyl-N-tert-butylnitrone