It is reported for the first time that the Wacker reaction can be carried o
ut smoothly in supercritical carbon dioxide or ROH/supercritical carbon dio
xide. Results show that both scCO(2) and co-solvent can remarkably affect t
he selectivity towards methyl ketone and the presence of ROH accelerates th
e reaction. The mechanism of the Wacker reaction in scCO(2) is also discuss
ed.