Thermal cyclizations of protonated poly-unsaturated aldehydes

Protonated 2,4-hexadienal (1H) and 2,4,6-octatrienal (2H), prepared by protonation of the analogous aldehydes in FSO 3 H, isomerized to give cyclized products 3H and 4H at 30 °C and −20 °C respectively. The rate constants for the cyclization of 1H were measured in both FSO 3 H and CF 3 SO 3 H. It was found that the rate constant for isomerization decreased when CF 3 SO 3 H was used as the reaction medium. It is suggested that the thermal …