Acid-catalyzed aza-Diels-Alder versus 1,3-dipolar cycloadditions of methyl glyoxylate oxime with cyclopentadiene |
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Authors: | Carlos AD Sousa José E Rodríguez-Borges Xerardo Garcia-Mera |
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Institution: | a CIQ-Departamento de Química, Faculdade de Ciências, Universidade do Porto, Rua do Campo Alegre, 687, 4169-007 Porto, Portugal b Departamento de Química Orgánica, Facultade de Farmacia, Universidade de Santiago de Compostela, E-15782 Santiago de Compostela, Spain c Departamento de Química Física, Facultade de Química, Universidade de Santiago de Compostela, E-15782 Santiago de Compostela, Spain |
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Abstract: | The acid-catalyzed 1,4- and 1,3-cycloadditions between methyl glyoxylate oxime (1) and cyclopentadiene were investigated using various Lewis and/or Bronsted acids at different temperatures in dichloromethane as solvent. Besides the expected new adducts, (±)-methyl (3-exo)-2-hydroxy-2-azabicyclo2.2.1]hept-5-ene]-3-carboxylate (2) and (±)-methyl (3-endo)-2-hydroxy-2-azabicyclo2.2.1]hept-5-ene]-3-carboxylate (3), a third adduct, (±)-methyl (1R,4R,5R)-(2-oxa-3-azabicyclo3.3.0]oct-7-ene)-4-carboxylate (4), whose formation can be explained by a 1,3-dipolar cycloaddition, was obtained. Yields and product ratios were found to be more dependent on the catalyst than on the temperature; these results and the stereochemistry of the adducts, confirmed by spectroscopic data (1H and 13C NMR) and by X-ray crystallography, were used to analyze and propose a mechanistic explanation for both cycloadditions. |
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Keywords: | Aza-Diels-Alder reaction 1 3-Dipolar cycloaddition Glyoxylate oxime Isoxazolidines 2-Hydroxy-2-azabicyclo[2 2 1]heptenes |
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