Isomeric oxazolylbutadienes are formed in the reaction of 2-chloropyridinium salt with piperidine at different temperatures.

The structure of isomers is evident from comparing the signals of butadiene protons in the NMR spectra of products obtained at different temperature

(A) Product obtained at 80oC (3h). 1E,3E-isomer.

(B) Product obtained at 80oC (1h). Mixture of 1E,3E- and 1E,3Z-isomers.

(C) Product obtained at 20oC (3h). 1E,3Z-isomer.