Microwave-assisted reactions of nitroheterocycles with dienes. Diels-Alder and tandem hetero Diels-Alder/[3,3] sigmatropic shift |
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Authors: | M. Victoria Gó mez,André s Moreno,Abel de Có zar,Antonio de la Hoz,Pilar Prieto |
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Affiliation: | a Departamento de Química Orgánica, Universidad de Castilla-La Mancha, E-13071 Ciudad Real, Spain b Kimika Organikoa Saila, Kimika Fakultatea, Universidad del País Vasco-Euskal Herriko Unibertsitatea, P.K. 1071, 20080 San Sebastián-Donostia, Spain |
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Abstract: | Diels-Alder cycloaddition of 3-nitro-1-(p-toluenesulfonyl)indole 1 with dienes 2-6 under microwave irradiation in solvent-free conditions gave carbazole derivatives after elimination of the nitro group and in situ aromatization. While 3-nitro-1-(p-toluenesulfonyl)pyrrole 11 afforded indole derivatives, 4-nitro-1-(p-toluenesulfonyl)pyrazole 13 with cyclohexadiene 2 did not afford the expected cycloadduct but instead gave 1-cyclohexen-2-ylpyrazole 16. This process occurred by hydrolysis of the 1-(p-toluenesulfonyl) group, protonation of the diene and nucleophilic addition of the pyrazolate ion, as elucidated by computational studies. Reaction of nitroindole 1 with cyclohexadiene 2 afforded exclusively the endo stereoisomer (10endo) in a tandem hetero Diels-Alder/[3,3] sigmatropic shift, as determined by computational calculations. |
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Keywords: | Microwave irradiation Diels-Alder Diels-Alder/[3,3] sigmatropic shift Computational studies |
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