Toward ideal carbon dioxide functionalization

This Perspective recapitulates recent developments of carbon dioxide utilization in carbon-carbon bond formation reactions, with an intention of paving a way toward sustainable CO₂-functionalization and its tangible applications in synthetic chemistry. CO₂ functionalization reactions possess intrinsic drawbacks: the high kinetic inertness and thermodynamic stability of CO₂. Numerous procedures for CO₂ utilization depend on energy-intensive processes (i.e. high pressure and/or temperature), often solely relying on reactive substrates, hampering its general applications. Recent efforts thus have been dedicated to catalytic CO₂-utilization under ambient reaction conditions, however, it is still limited to a few activation modes and the use of reactive substrates. Herein, ideal CO₂-functionalization with particular emphasis on sustainability will be discussed based on the following sub-categories; (1) metal-catalyzed 'reductive' carboxylation reaction of halides, olefins and allyl alcohols, (2) photochemical CO₂-utilization, (3) redox-neutral CO₂-functionalization, and (4) enantioselective catalysis incorporating CO₂ to form C-CO₂ bonds (excluding strain mediated reactions with epoxide- and aziridine-based substrates). Recent progress in these fields will be discussed with the proposed reaction mechanisms and selected examples, highlighting redox-neutral, umpolung, and asymmetric carboxylation to postulate ideal CO₂ functionalization reactions to be developed in the near future.