Organic Synthesis. 2005, 11, 107. DOI: 10.1002/0471264229.os081.21
◆An efficient and environmentally benign method for oxidizing primary alcohols to carboxylic acids using stoichiometric NaClO2, catalytic TEMPO, and NaOCl was developed by Merck.
◆The remarkable acceleration by catalytic NaClO can be explained by the proposed catalytic cycle.
◆The long induction period of the reaction without a catalytic amount of bleach is likely due to the relatively slow oxidation of TEMPO radical or the hydroxylamine D by NaClO2. Once the reaction is initiated, it becomes selfsustaining as NaOCl is continuously regenerated. The chlorination problem is greatly reduced because the concentration of NaOCl remained low throughout the reaction. Risks for epimerization of the neighboring chiral center are also reduced since the labile aldehyde intermediate is rapidly oxidized to the carboxylic acid by sodium chlorite.
◆This method is mild and efficient and has been demonstrated on a variety of primary alcohols.
◆It appeared that carbon-carbon triple bonds can be tolerated, but substrates with ordinary carbon-carbon double bonds such as cinnamyl alcohol failed to react. This was likely due to quenching of the catalytic NaOCl, which shut down the catalytic cycle.
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