Methods for the introduction of a Phenylselenium Dichloride Group into he α-position of Carbonyl Compounds. Syntheses of Enones.

Article abstract of DOI:10.1021/jo00252a028

Phenylselenium trichloride, PhSeCl3, direcly introduced, in fair yield, a PhSeCl2 group into the α-position of ketones with loss of HCl.To some extent, depending on the substrate, this reagent was also shown to act as a chlorinating agent toward ketones, yielding α-chloro ketones and α-phenylselenenyl ketones.The latter compounds were readily converted to selenium(IV) dichlorides by SO2Cl2 chlorination to significantly improve the overall yields of the selenetion process.The consecutive treatment of ketones with PhSeCl and SO2Cl2 could also be used for the introduction of a PhSeCl2 group, but this procedure was usually less efficient than the PhSeCl3-based one.Unsymmetrical ketones were selenated with poor regiocontrol.Aldehydes were primarily chlorinated by treatment with PhSeCl3, but consecutive treatment with PhSeCl3 and SO2Cl2 introduced a PhSeCl2 group into the α-position.Carboxylic acids and esters were ureactive toward PhSeCl3 and PhSeCl.PhSeCl3 underwent addition reactions with enones to introduce a PhSeCl2 group α or β to the carbonyl group, depending on the substrate.The carbonyl compounds substituted in the α-position with a PhSeCl2 group were easily converted to the corresponding α,β-unsaturated carbonyl compounds after hydrolysis/selenoxide elimination.Since the selenium(IV) intermediates involved were highly crustalline and easy to purify, the preparation of enones from symmetrical ketones via PhSeCl2 introduction/hydrolytic elimination was especially convenient to perform from the operational point of view.