Reactions of 1,2,4‐Oxadiazole[4,5‐a]piridinium Salts with Alcohols: the Synthesis of Alkoxybutadienyl 1,2,4‐Oxadiazoles

1,2,4-Oxadiazole[4,5-a]piridinium salts add alcohols and alkoxides
to undergo electrocyclic ring opening affording alkoxybutadienyl
1,2,4-oxadiazole derivatives. The pyridinium salts
represent a special class of Zincke salts that are prone to
rearrange to give alkoxybutadienyl 1,2,4-oxadiazoles when
treated with suitable nucleophiles or, alternatively, to give
pyridones in the presence of bicarbonate. The pivotal tuning of
the experimental conditions leads to a straightforward synthesis
of valuable 1,2,4-oxadiazole derivatives. The mechanism is also
discussed in the light of previous observations.