Competitive demethylation and substitution in N,N,N-trimethylanilinium fluorides |
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Authors: | Haoran Sun |
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Institution: | Department of Chemistry and Nebraska Center for Materials and Nanoscience, University of Nebraska, Lincoln, NE 68588-0304, USA |
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Abstract: | Fluorination of aromatic compounds by nucleophilic displacement of trimethylanilinium salts by fluoride is a commonly used reaction for radiotracer synthesis. Though the liberated trimethylamine is thought to be an excellent leaving group for this type of SNAr reaction, scattered reports show that amine demethylation (reverse Menschutkin reaction) sometimes dominates over substitution, particularly when relatively electron rich fluoroarenes are the desired targets. Here we provide systematic experimental and theoretical studies of trimethylanilinium demethylation and substitution. Results from these studies highlight the limits of this leaving group in fluoroarene synthesis and have important ramifications for the design of nucleophilic fluorinating agents featuring ammonium cations. |
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Keywords: | Tetrabutylammonium fluoride Amine deprotection Demethylation Nucleophilic substitution SN2 SNAr Arene fluorination PET Leaving groups Reverse Menschutkin |
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