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15.1.1.1.3.1.4 Method 4: From 1-(2-Oxoalkyl)pyridinium (or Quinolinium/Isoquinolinium) ­Compounds, α,β-Unsaturated Carbonyl Compounds, and Ammonium Salts

DOI: 10.1055/sos-SD-015-00002

Spitzner, D.Science of Synthesis, (20051523.

Kröhnke compounds 42 [1-(2-oxoalkyl)pyridinium or quinolinium/isoquinolinium compounds] possess both an enhanced CH acidity and a good leaving group at the α-position of the ketone. 1-(2-Oxoalkyl)pyridinium (or quinolinium/isoquinolinium) compounds are obtained using the OrtolevaKing reaction, can be easily deprotonated, and add to the Michael acceptor (or its precursor, the Mannich salt 41) to give an intermediate which condenses with an ammonium salt and aromatizes by expelling the leaving group (pyridine, quinoline/isoquinoline) to form pyridines. This method is very useful for the synthesis of oligopyridines, e.g. 43,[‌51‌] or aryl-substituted pyridines (Scheme 15).[‌84‌‌87‌]

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