Carbanion reactivity — σ-adduct formation and elimination in the reactions of the carbanion from bis(phenylsulfonyl)methane with 4-nitrobenzofurazan derivatives

Abstract

1H NMR studies in [2H6]-DMSO show that the carbanion 4 from bis(phenylsulfonyl)methane reacts with 4,6-dinitrobenzofuroxan to yield a σ-adduct that undergoes base-catalysed elimination to yield an alkene derivative. Rate constants, measured spectrophotometrically, are reported for the corresponding reactions in methanol of 4 with 4-nitrobenzofurazan and some derivatives that give adducts at the 5-position. The intrinsic rate constant, ko, for this process has a value of 1.5 ± 0.5. The 5-adducts undergo methoxide-catalysed elimination of phenylsulfinic acid to yield alkene derivatives and rate constants for this process are reported.Key words: carbanions, 4-nitrobenzofurazan, σ-adducts, elimination reactions.