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Linear free energy ortho-correlations in the reactions of some 2-bromo-5-nitro-3-X-thiophenes with primary and secondary amines in benzene

2002; Royal Society of Chemistry; Issue: 5 Linguagem: Inglês

10.1039/b111544h

1472-779X

Giovanni Consiglio, Vincenzo Frenna, Susanna Guernelli, Gabriella Macaluso, Domenico Spinelli,

Synthesis and Biological Evaluation

The kinetics of SNAr reactions of some 2-bromo-3-X-5-nitrothiophenes (X = Me, H, Br, CONH2, CO2Me, COMe, SO2Me, CN and NO2) with some primary (n-butylamine and benzylamine) and secondary (pyrrolidine, piperidine, morpholine and N-benzylamine) amines have been measured in benzene as a function of nucleophile concentration. Most of the reactions studied show apparent kinetic constants little affected or not affected by an increase in amine concentration, indicating that the overall reaction rate is controlled by the formation of the reaction intermediate. The reactions of the substrates where X = Br and CN with the two primary amines proved to be base-catalysed. The k3B/k−1 values calculated for these substituents are inconsistent with the hypothesis of a base catalysis for the intermediate decomposition and strongly suggest a catalysis of the first step of the reaction pathway.