Terminal
acetals were selectively synthesized from various unbiased
aliphatic terminal alkenes and 1,2-, 1,3-, or 1,4-diols using a PdCl2(MeCN)2/CuCl catalyst system in the presence of p-toluquinone under 1 atm of O2 and mild reaction
conditions. The slow addition of terminal alkenes suppressed the isomerization
to internal alkenes successfully. Electron-deficient cyclic alkenes,
such as p-toluquinone, were key additives to enhance
the catalytic activity and the anti-Markovnikov selectivity. The halogen
groups in the alkenes were found to operate as directing groups, suppressing
isomerization and increasing the selectivity efficiently.
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.
1,1-Disubstituted alkenes feature high steric hindrance, which renders their Wacker-type oxidation difficult. We demonstrated the stereoselective synthesis of 2-hydroxytetrahydrofurans via the Wacker-type oxidation of 3-methyl-3-buten-1-ols by using a PdCl2(MeCN)2/NO/BQ catalyst...
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