- Anionic ?-complexes as biochemical and biophysical probes. Part 5. The interactions of dopamine derivatives with 1,3,5-trinitrobenzene
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The interaction of the ambident nucleophile dopamine, liberated from its hydrochloride salt by treatment with assorted bases, with 1,3,5-trinitrobenzene (TNB) in dimethyl sulfoxide (DMSO), has been investigated.Use of triethylamine or 1,4-diazabicyclooctane as the external base, leads to little reaction.With 1 equivalent of dimsyl anion relative to dopamine hydrochloride, reaction with TNB affords initially the N-bonded anionic ?-complex 3, which transforms into the C-bonded adduct 6 in a slower reaction. 3,4-Di-O-methyldopamine reacts with TNB to give only an N-adduct, 9, which is structurally-related to 3.Similar results are obtained in the reaction system in which the dopamine hydrochloride is first treated with 2 or more equiv of dimsyl anion.In all cases, 5, the anticipated product of O-attack, is unobserved.The reaction sequence thus involves the reversible formation of a nitrogen-centered adduct in a kineticaly controlled process, followed by the slow but effectively irreversible formation of the carbon-bonded adduct in a thermodynamically preferred process.The results are considered in terms of an energy profile which shows the pathways for formation of the observed species 3 and 6, as well as the putative O-adduct, 5.Further, comparison of the present results with those found in other ambident systems suggests that the products of C-attack are thermodynamically favoured over those which arise from attack via the heteroatom(s) of the nucleophile, independent of the nature of the heteroatom (O or N) nucleophilic centre(s).
- Buncel, Erwin,Dust, Julian M.,Manderville, Richard A.,Park, Kuk-Tae,Ony Do, Ikenna
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p. 371 - 376
(2007/10/02)
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