Intramolecular Diels-Alder reactions of quaternary pyrazinium salts and protonated pyrazinium cations. Synthesis of annelated pyridinium salts and annelated pyridines.
✍ Scribed by Bart Geurtsen; Dick A. de Bie; Henk C. van der Plas
- Publisher
- Elsevier Science
- Year
- 1989
- Tongue
- French
- Weight
- 807 KB
- Volume
- 45
- Category
- Article
- ISSN
- 0040-4020
No coin nor oath required. For personal study only.
✦ Synopsis
Quaternization of alkynyl substituted pyrazines with triethyloxonium tetrafluoroborate in dichloromethane occurs exclusively at N-4 yielding 3-alkynyl-lethylpyrazinium salts, as shown by the 13C NMR data. Protonation of the same pyrazines with trifluoroacetic acid also occurs at N-4. The quaternary as well as the protonated pyrazines undergo an intramolecular Die E yrazinium salts -Alder reaction under considerably milder conditions than the corresponding neutral pyrazines. The products of the reactions were @annelated quaternary pyridinium salts and [cJannelated protonated pyridinium cations, respectively.