Biomimetic catalysis of S_N2 reactions through cation-π interactions. The role of polarizability in catalysis

Abstract

Cyclophane hosts 1 and 2 have been shown to be effective catalysts for both the alkylation of quinoline structures to produce quinolinium salts and the dealkylation of sulfonium salts to produce sulfides. Thus, reactions that develop positive charge in the transition state and reactions that destroy positive charge are accelerated. The former observation is not surprising, given the well-documented ability of these hosts to bind cations through the cation-π interaction. The catalysis of the dealkylation reactions, however, along with several other observations, suggests that some other factor is involved in the catalysis. It is proposed that the high polarizability of the transition states is well matched to the very polarizable hosts and that this contributes to the catalysis.

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