A high yielding three-component reaction between β-iodo ethylamine derivatives, MeOH and gaseous CO₂ at ambient temperatures and pressures is reported using silver(I) oxide. Unfunctionalised alkyl iodides were also found to be effective in this transformation and their optimisation is also described. To highlight the ease and control with which gaseous CO₂ can be captured and functionalised under mild conditions, the reaction was performed using ¹³C-enriched CO₂ to afford specifically ¹³C-carbonyl-labelled dialkyl carbonates with exquisite control of the isotopic purity in good yields and without the need for specialised equipment.