Abstract
The dimethylchloronium salt [Me2Cl][Al(OTeF5)4] is used to methylate electron‐deficient aromatic systems in Friedel–Crafts type reactions as shown by the synthesis of N‐methylated cations, such as [MeNC5F5]+, [MeNC5F4I]+, and [MeN3C3F3]+. To gain a better understanding of such fundamental Friedel–Crafts reactions, the role of the dimethylchloronium cation has been evaluated by quantum‐chemical calculations.
Highlights
The Friedel–Crafts alkylation is a well-known and widely used and challenging synthetic tool.[1]
The Friedel–Crafts alkylation reaction is based on the polarization of an alkyl halide by a Lewis acid like AlCl3 which further reacts as an electrophilic reagent for example, with an aromatic molecule to form an arenium ion (Wheland intermediate, Scheme 1, top).[2]
In this work we report on the role of the dimethylchloronium cation in Friedel–Crafts type methylation reactions, especially in the system MeCl–AlCl3; and the reaction of 1 with electron-deficient aromatic systems
Summary
The Friedel–Crafts alkylation is a well-known and widely used and challenging synthetic tool.[1]. CH3+ cation[3] is low, Olah and DeMember suggested the formation of the dimethylchloronium cation as an intermediate for Friedel–Crafts reactions[4] and isolated [Me2Cl] [SbF6][5] as a thermally labile compound. The only other known anion which is able to stabilize the dimethylchloronium cation so far is the carborate anion [CHB11Cl11]À. The salt [Me2Cl] [CHB11Cl11] is considerably more thermally stable.[6] We recently synthesized the accessible and room temperature-stable dimethylchloronium salt [Me2Cl][Al(OTeF5)4] (1, see Scheme 1 bottom).[7]. In this work we report on the role of the dimethylchloronium cation in Friedel–Crafts type methylation reactions, especially in the system MeCl–AlCl3; and the reaction of 1 with electron-deficient aromatic systems
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