New, Efficient Synthesis of -Chloroketones Using SiCl4/Urea-Hydrogen Peroxide or SiCl4/Iodosylbenzene Reagent Systems

[image omitted] Alkyl aryl ketones on treatment with SiCl4/urea-hydrogen peroxide (UHP) or SiCl4/iodosylbenzne reagent systems afforded -chloroketones in excllent yields, while ketones with higher enol content provide exclusively ,-dichloroketones under exceedingly mild conditions. The reaction proceeds via the initial formation of silyl enol ethers. A polarized chlorine intermediate that resulted from the coordination of SiCl4 with the in situ formed trichlorosilyl hypochlorite Cl3SiOCl is thought to be the active chlorinating agent.