Development of New Methods for Carbonylation by Free-Radical Reactions

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A novel carbonylation method based on free-radical reactions has been developed. Acylradicals, generated by the addition of alkyl free-radicals to carbon monoxide, have been effectively trapped by tin hydride. Through this sequence, the free-radical formylation of organo halides to the corresponding aldehydes was realized. When an alkene was also present in the reaction system, the trapping of the alkyl free-radical by carbon monoxide to form an acyl free-radical and the subsequent addition of that radical to the alkene took place efficiently to give and unsymmetrical ketone. Tris(trimethylsily)silane can also be used for a free-radical mediator. This sequence represents a unique method for the double alkylation of carbon monoxide. Carbonylative cyclizations to give cyclopentanones can also be affected starting with 4-pentenyl halides. All of these findings that free-radical carbonylation is useful method for the introduction of carbon monoxide into organic molecules.