Palladium(II) and palladium(0)-cocatalyzed ring opening and oxidation reactions of 2-(arylmethylene)cyclopropylcarbinols

In the presence of Pd(II) acetate and triethylamine as well as triphenylphosphine, 2-(arylmethylene)cyclopropylcarbinols 1 underwent ring opening and oxidation reactions smoothly to deliver (2E,4E)-5-arylpenta-2,4-dienals 2 in toluene at 60 °C in moderate to good yields under ambient atmosphere. Mechanisms involved with an in situ generated Pd(0) species from Pd(II) and Et3N or PPh3 catalyzed isomerization of 1 to provide (E,E)-5-arylpenta-2,4-dien-1-ols 3 and following a Pd(II) catalyzed aerobic oxidation of 3 have been proposed on the basis of control and deuterium labeling experiments.