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

H-1 NMR studies in DMSO-d(6) of the reaction of benzyltriflones, 2, with 4,6-dinitrobenzofuroxan, 4, indicate the formation, with or without the presence of added base, of anionic sigma-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 sigma-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 beta 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 (C) 2007 John Wiley & Sons, Ltd.