Halogenation of Aldehydes and Ketones by Selenium (IV) Oxyhalides Generated in-situ from Selenium Dioxide and Halotrimethylsilanes

Bromo-and chlorotrimethylsilane react with selenium dioxide in halocarbon solvents and generate selenium oxybromide and oxychloride, respectively. These in-situ generated oxyhalides turned out to be very efficient for selective bromination and chlorination of aldehydes and ketones. Under carefully controlled reaction conditions, second and third introduction of halogens into carbonyl compounds can be greatly suppressed, and high yields of monohalo compounds were obtained. The product ratios of this halogenation reactions can be best explained if the reactions are assumed to involve intermediate β-ketoselenenyl chlorides.