^1H NMR and kinetics studies of the reaction of 4-methyl, 4-bromo and 3-trifluoromethyl benzyltriflones with aromatic nitro-compounds

Rate measurements are reported for the reactions in methanol of carbanions derivedfrom benzyltriflones, 2a–c, with 4-nitrobenzofurazan derivatives, 4a and 4b, to give anionic σ-adducts.^1H NMR studies in DMSO-d6 of the reaction of benzyltriflones, 2, and 4-nitrobenzofurazan, 4a, in the presence of triethylamine are consistent with products formed by the elimination of trifluoromethyl sulfinic acid from r-adducts initially formed by carbanion attack at the 5-position of 4a. Evidence for the high steric requirements of the benzyltriflone anions come from the low value of β; the slope of the linear plot of values of log k5 versus pKa.