Deprotection by electrolysis: Part I. The application of homogeneous redox catalysis to the study of the reduction of tosyl esters and amides |
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Authors: | HLS Maia MJ Medeiros MI Montenegro D Court D Pletcher |
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Institution: | Centro de Quimica Pura e Aplicada da Universidade do Minho, Largo do Paço, 4719 Braga Codex, Portugal;Department of Chemistry, The University Southampton, SO9 5NH, England |
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Abstract: | The mechanism of the cathodic cleavage of tosylate protecting groups from alcohols, amines and phenols in dimethylformamide has been probed using the technique of homogeneous redox catalysis. Some nine tosyl esters and six tosyl amides have been investigated and it is confirmed that these deprotection reactions occur by cleavage of the anion radicals. The formal electrode potentials for the couples, neutral molecule/anion radical, are reported and it is shown that the rate constants for the cleavage of the anion radicals lie in the range 104 s?1 to >108 s?1. Indeed for aromatic amines and phenols, the homogeneous charge transfer between the catalyst and the substrate becomes the rate determining step. |
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