Abstract
Quaternization of alkynyl substituted pyrazines with triethyloxonium tetrafluoroborate in dichloromethane occurs exclusively at N-4 yielding 3-alkynyl-1-ethylpyrazinium salts, as shown by the 13C NMR data. Protonation of the same pyrazines with trifluoroacetic acid also occurs at N-4. The quaternary pyrazinium salts as well as the protonated pyrazines undergo an intramolecular Diels-Alder reaction under considerably milder conditions than the corresponding neutral pyrazines. The products of the reactions were [ c ]-annelated quaternary pyridinium salts and [ c ]-annelated protonated pyridinium cations, respectively.
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