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We present the intra- and inter-molecular organocatalysis of S N 2 fluorination using CsF by crown ether to estimate the efficacy of the promoter and to elucidate the reaction mechanism. The yields of intramolecular S N 2 fluorination of the veratrole substrates are measured to be very small (&lt;1% in 12 h) in the absence of crown ether promoters, whereas the S N 2 fluorination of the substrate possessing a crown ether unit proceeds to near completion (~99%) in 12 h. We also studied the efficacy of intermolecular rate acceleration by an independent promoter 18-crown-6 for comparison. We find that the fluorinating yield of a veratrole substrate (leaving group = -OMs) in the presence of 18-crown-6 follows the almost identical kinetic course as that of intramolecular S N 2 fluorination, indicating the mechanistic similarity of intra- and inter-molecular organocatalysis of the crown ether for S N 2 fluorination. The calculated relative Gibbs free energies of activation for these reactions, in which the crown ether units act as Lewis base promoters for S N 2 fluorination, are in excellent agreement with the experimentally measured yields of fluorination. The role of the metal salt CsF is briefly discussed in terms of whether it reacts as a contact ion pair or as a "free" nucleophile F - .

Inter- and Intra-Molecular Organocatalysis of SN2 Fluorination by Crown Ether: Kinetics and Quantum Chemical Analysis