The electrophilicity parameters (E) of some trifluoromethylthiolating and difluoromethylthiolating reagents were determined by following the kinetics of their reactions with a series of enamines and carbanions with known nucleophilicity parameters (N, sN ), using the linear free-energy relationship log k2 =sN (N+E). The electrophilic reactivities of these reagents cover a range of 17 orders of magnitude, with Shen and Lu's reagent 1 a being the most reactive and Billard's reagent 1 h being the least reactive electrophile. While the observed electrophilic reactivities (E) of the amido-derived trifluoromethylthiolating reagents correlate well with the calculated Gibbs energies for heterolytic cleavage of the X-SCF3 bonds (Tt+ DA), the cumol-derived reagents 1 f and 1 g are more reactive than expected from the thermodynamics of the O-S cleavage. The E parameters of the tri/difluoromethylthiolating reagents derived in this work provide an ordering principle for their use in synthesis.
Keywords: difluoromethylthiolation; electrophilicity; linear free-energy relationships; structure-reactivity relationships; trifluoromethylthiolation.
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