Transition Metal‐Free Carboxylation of Aryl Boronates in Supercritical CO2

Carboxylation using stable and abundant CO₂ as a carbon source is an attractive option in synthetic organic chemistry if the use of highly reactive organometals or toxic and expensive transition metals can be avoided. Herein a transition metal‐free direct carboxylation of aryl trialkoxyboronates in supercritical CO₂ (scCO₂), promoted by a catalytic amount of ZnO, is reported. The use of cage‐shaped trialkoxyboronates, which are both nucleophilic and soluble in scCO₂, is the key to this reaction. density functional theory 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.