Reactions of 1-amino-2,4,6-triphenylpyridinium cations with α,β-unsaturated compounds synthesis of highly substituted pyrazolo [1,5-a]pyridine derivatives

N-Amino pyridinium salts in organic synthesis

“…29 To overcome this challenge, a two-step protocol was employed based on initial reaction of pyrylium salt 9 with 2-aminopyridine to afford pyridinium salt 11 followed by subsequent hydrazinolysis to form the desired N-aminopyridinium salt 12 (Scheme 6c). 30 Condensation of unsubstituted pyrylium salts with simple hydrazine has not been reported to our knowledge, however, Studer et al reported the reaction of unsubstituted pyrylium salt 13 with N-aminophthalimide 14 to afford N-aminopyridinium salt 15 (Scheme 6d). 31 Several N-alkyl or N-acyl aminopyridinium salts have been synthesized by condensation of pyrylium salts with mono-or di-substituted hydrazines.…”