Palladium-catalyzed oxidation of primary alcohols: Highly selective direct synthesis of acetals

Selective direct synthesis of symmetric acetals through a tandem aerobic oxidation–acetalization of primary alcohols, using a chloride-free Pd(OAc)2/Cu(OAc)2/p-TsOH system as an efficient bifunctional catalyst, has been developed. The reactions occur in neat alcohols with no use of other solvent under mild conditions (50–80 °C, 1–10 atm). p-Toluenesulfonic acid exerts a great accelerative and catalyst stabilizing effect, showing a synergism with Cu(OAc)2. Bimetallic Pd–Cu catalysis is suggested in these reactions. Under similar conditions, a secondary alcohol, propanol-2, reacts more slowly giving mainly acetone. Conventional palladium catalytic systems, such as PdCl2/CuCl2, Pd(OAc)2/LiNO3, and Pd(OAc)2/pyridine, showed no or very low activity in the oxidation of neat n-butanol.

Graphical abstractSelective direct synthesis of acetals through a tandem oxidation–acetalization of primary alcohols, using a chloride-free Pd(OAc)2/Cu(OAc)2/p-TsOH system as an efficient bifunctional catalyst, has been developed. The reaction occurs in neat alcohols with no use of other solvent under mild aerobic conditions. p-Toluenesulfonic acid (p-TsOH) and Cu(OAc)2 exert a great synergetic effect on the reaction rate and selectivity for acetals.Figure optionsDownload full-size imageDownload as PowerPoint slide