Tri(hetero)substituted Carbonium Ions. II. 2-Dialkylamino-1,3-dithiolanylium Ions. Reactions with Nucleophiles and Ambident Behaviors

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Abstract
The reactions of 2-dialkylamino-1,3-dithiolanylium perchlorates with a variety of nucleophilic species including oxygen, sulfur and nitrogen nucleophiles have been investigated. Examination of the isolated products reveals that these trihetrosubstituted carbonium ions behave as ambident electrophiles toward nucleophiles with two reactive sites, i.e., the electron-deficient centered carbon (a) and the ring-methylene carbon atom (b), and that the nature of nucleophiles greatly affects the reaction course in a straightforward manner. The reaction course may be classified as follows. If the nucleophile is basic, the reaction at the site (a) (mode A) is favored, but if it has large sub-stituents, the initial proton abstraction reaction (mode C) is predominant, while if the nucleophile is polarizable, the reaction at the site (b) (mode B) is favored. The major factor deciding the reaction course is discussed in terms of the schematic energy profile of the overall reaction.

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