Progress in organometallic catalysis began with the discovery of the Roelen reaction (hydroformylation with carbon monoxide and hydrogen) in 1938 and the Reppe reaction (hydrocarboxylation with carbon monoxide and water) in 1939. Since then, carbonylation chemistry by using carbon monoxide has occupied a central position in organometallic chemistry, as it relates to organic synthesis. There is, however, the problem of using gaseous carbon monoxide (a toxic greenhouse gas) in this chemistry. Recently, some strategies that address this issue have appeared. This minireview describes carbonylation reactions that can be conducted without the direct use of carbon monoxide. These carbonylation reactions provide reliable and accessible tools for synthetic organic chemists.

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The reaction of enynes with aldehydes in the presence of a catalytic amount of [RhCl(cod)](2)/dppp results in the Pauson-Khand-type reaction without the use of gaseous carbon monoxide to give bicyclic cyclopentenones in high yields (14 examples). Aldehydes serve as a source of carbon monoxide, and their carbonyl moiety is transferred to enynes, resulting in the formation of the carbonylated products. This reaction represents the first example of a CO-transfer carbonylation.

The rhodium(I)-catalyzed reaction of alkynes with 2-bromophenylboronic acids in the presence of paraformaldehyde resulted in a CO gas-free carbonylative cyclization, yielding indenone derivatives. [RhCl(BINAP)](2) and [RhCl(cod)](2) were responsible for the decarbonylation of formaldehyde and the subsequent carbonylation of alkynes with 2-haloboronic acids, respectively, leading to efficient whole carbonylation. Sterically bulky and electron-withdrawing groups on unsymmetrically substituted alkynes favored the alpha-position of indenones.