Palladium/Copper‐catalyzed Oxidation of Aliphatic Terminal Alkenes to Aldehydes Assisted by p‐Benzoquinone

The development of an anti‐Markovnikov Wacker‐type oxidation for simple aliphatic alkenes is a significant challenge. Herein, a variety of aldehydes can be selectively obtained from various unbiased aliphatic terminal alkenes using PdCl2(MeCN)2/CuCl in the presence of p‐benzoquinone (BQ) under mild reaction conditions. Isomerization of the terminal alkene to the internal alkene was suppressed via slow addition of the starting material to the reaction mixture. In addition to the Pd catalyst, CuCl and BQ were essential in order to obtain the anti‐Markovnikov product with high selectivity. Terminal alkenes bearing a halogen substituent afforded their corresponding aldehydes with high anti‐Markovnikov selectivity. The halogen acts as a directing group in the reaction. DFT calculations indicate that a μ‐chloro Pd(II)−Cu(I) bimetallic species with BQ coordinated to Cu is the catalytically active species in the case of a terminal alkene without a directing group. Anti‐Markovnikov Wacker‐type oxidation: Aldehydes were selectively obtained from various unbiased aliphatic terminal alkenes using PdCl2(MeCN)2/CuCl in the presence of p‐benzoquinone under mild reaction conditions.