General methods for the synthesis of styrylpyridinium salts (microreview)

This microreview covers the general methods on the synthesis of mono-, bis-, and tristyrylpyridinium fluorophores described in the literature in recent years. A summary of the most common synthesis can be divided into four distinct methods: aldol condensation followed by N-alkylation of pyridine moiety, Knoevenagel condensation reaction of picolinium salt and aldehyde, Wittig reaction of triphenylphosphine salt and pyridine aldehyde followed by N-alkylation of pyridine moiety, and Horner reaction between bisphosphonate derivative and 4-pyridinecarboxaldehyde followed by N-alkylation of pyridine moiety. Metal-catalyzed reactions were not reviewed. The microreview primary focuses on the synthesis of styrylpyridinium salts having in their structures a 4-pyridinium moiety.