Transition‐Metal‐Free Carboxylation of Aryl Boronates in Supercritical CO2

Carboxylation using stable and abundant CO2 as a carbon source would be an attractive option in synthetic organic chemistry if the use of highly reactive organometals or toxic and expensive transition metals can be avoided. Herein we report a transition‐metal‐free direct carboxylation of aryl trialkoxyboronates in supercritical CO2 (scCO2), promoted by a catalytic amount of ZnO. The use of cage‐shaped trialkoxyboronates, which are both nucleophilic and soluble in scCO2, is the key to this reaction. DFT calculations indicate that the high pressure and high temperature of scCO2 with the ZnO catalyst compensate for the high activation energy of direct carboxylation of the boronates.