DFT investigation of the triphenylphosphine-assisted electrochemical dehydroxylative transformations

Abstract

The mechanism of the dehydroxylative transformations to form CN and Chalogen bonds assisted by triphenylphosphine via electrochemical method was investigated by DFT calculation. It involved a two-step oxidation process of Ph3P to generate alkoxy phosphonium intermediate, which would be attacked by the nucleophiles. In the case of the alcohols containing heteroatoms to the α-carbon, such as N or O, the alkoxy phosphoniums released Ph3PO to produce the stable alkyl cations, which could be trapped by the nitrogen-based nucleophiles to construct the Csp3N bond. Otherwise, the alkoxy phosphoniums could be directly attacked by the nucleophiles, such as Cl- and Br-, following the classical SN2 mechanism, to form Chalogen bonds. In contrast, no fluorinated product could be obtained through this strategy due to the preferential attack of F- at the phosphorus, leading to the phosphorane intermediate to liberate the original alcohols.