Carbanion reactivity; studies of σ‐adduct formation from benzyltriflone anions and 4‐nitrobenzofurazan derivatives |
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Authors: | Basim H. M. Asghar Michael R. Crampton |
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Affiliation: | 1. Chemistry Department, Durham University, Durham DH1 3LE, UK;2. Chemistry Department, Durham University, Durham DH1 3LE, UKDepartment of Chemistry, University of Durham, Science Laboratories, South Road, Durham DH1 3LE, UK.=== |
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Abstract: | 1H NMR studies in DMSO‐d6 of the reaction of benzyltriflones, 2 , with 4,6‐dinitrobenzofuroxan, 4 , indicate the formation, with or without the presence of added base, of anionic σ‐adducts. Spectra obtained from solutions of 2 and 4‐nitrobenzofurazan, 6a , in the presence of triethylamine are consistent with products formed by the elimination of trifluoromethylsulfinic acid from σ‐adducts initially formed by carbanion attack at the 5‐position of 6a . Kinetic studies of the latter reaction in methanol allow the determination of rate constants for nucleophilic attack by the carbanions at the 5‐position. The low value of β for these reactions together with the failure to observe reaction with 1,3,5‐trinitrobenzene suggest that the benzyltriflone anions have unusually large steric requirements. Copyright © 2007 John Wiley & Sons, Ltd. |
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Keywords: | carbanions nucleophilic reactivity sigma‐adducts elimination reactions 4‐nitrobenzofurazan |
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