Heterocyclic Betaines. 14. (E)-1-Alkyl-dihydropyridines with a Betaine Character. An Improved Protocol for a Knoevenagel-Type Condensation for Synthesis of (E)-1-Alkyl-pyridinium Salts

Article abstract of DOI:10.1021/jo00044a015

A novel class of aza analogues of (E)-stilbene, the (E)-1-alkyl-<2-(imidazol-2-ylidene)ethylidene>dihydropyridines 4A <-> 4B, 5A <-> 5B, have been studied.They were synthesized by a convenient two-steps procedure.In each of the steps, the necessary basic reaction medium has been generated by a strong basic ion-exchange resin (OH(-)-form).Thus, a modified protocol of the Knoevenagel condensation has been applied to preparation of the title (imidazolylvinyl)pyridinium salts, deprotonation of which yields several examples of compounds 4 and 5.The betaine character of 4 and 5 is well reflected by their physicochemical properties and reactivity toward electrophiles (MeI).