deuterocarboxylation with tetrabutylammonium oxalate as the carbonyl source and D2O as the deuteration agent was described. For the first time, the oxalic salt acted as both the reductant and carbonyl source through single electron transfer and subsequential homolysis of the C–C bond. The strongly reductive CO2 radical anion species in situ generated from oxalate played significant roles in realizing the global