Carbonyl group-containing organometallic intramolecular-coordination five-membered ring compounds are easily synthesized by the following five reaction methods: (1) cyclometalation, especially, orthometalation reactions; (2) the reactions of the moieties of an unsaturated carbon-carbon bond attached to a carbonyl group (C C-CO, C C-CO); (3) the reactions of an unsaturated carbon-carbon bond with carbon monoxide (C C and CO, C C and CO); (4) carbonylative ring expansion reactions; and (5) others. These compounds are very easily and regio-specifically synthesized with many kinds of metal compounds, including both transition metals and main group metals. Many of such the reactions are easily applied to organic syntheses.