The reactivity of 2-vinylindoles with dimethyl acetylenedicarboxylate |
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Authors: | R Alan Jones Pilar Martinez Fresneda Teresa Aznar Saliente José Sepúlveda Arques |
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Institution: | School of Chemical Sciences, University of East Anglia, Norwich NR4 7TJ, U.K.;Departamento de Quimica Organica, Facultad de Farmacia, Universidad de Valencia, Valencia Spain |
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Abstract: | The overall rates of reaction of 1-substltuted-1- (1-methyl-2-indolyl)ethenes with dimethyl acetylenedicarboxylate are considerably lower than those of the corresponding 2-vinyl- pyrroles. Steric interaction between the N-methyl group on the indole ring and the 1-substituent on the ethenyl group prevents the diene system adopting a coplanar configuration and, thereby, inhibits the π4 + π2 cycloaddition reaction of the system with dimethyl acetylenedicarboxylate. Under such conditions, the indolylethene preferentially undergoes a Michael addition reaction at the 3-position. The π4 + π2 cycloaddition reaction is promoted at elevated temperatures. No evidence was found for a Cope rearrangement of the Michael adducts to give the dihydrocarbazole. |
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