4-(Dimethylamino)benzaldehyde is alkylated at the N atom by dialkyl sulfates, MeI, or Me 3O BF 4. In contrast, ethylation by Et 3O BF 4 occurs selectively at the O atom yielding a quinoid iminium ion. 4-(Diethylamino)benzaldehyde is alkylated only at O by either Et or Me oxonium reagent. The iminium salts are prone to hydrolysis giving the corresponding hydrotetrafluoroborates. Five crystal structures were determined.
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