Carbanion reactivity; studies of σ-adduct formation from benzyltriflone anions and 4-nitrobenzofurazan derivatives

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. 1H NMR studies in DMSO‐d6 show that benzyltriflone anions react at the 5‐position of 4‐nitrobenzofurazan to give σ‐adducts which rapidly eliminate trifluoromethylsulfinic acid. Kinetic studies in methanol allow the nucleophilicities of the anions to be evaluated.