Halogens, silyl enolate oxidation

Chemical oxidation of silyl enolates has been performed with a variety of inorganic and organic oxidants such as ozone, copper(II) salts, Pb(OAc)4, Ag20, hypervalent iodine compounds such as iodosobenzene in methanol, (NH4)2[Ce(N03)6], xenon difluoride, tetranitromethane, halogens, nitronium-, diazonium- and triphenylmethyl salts, chloranil and ddq. 

Silyl enolates are useful starting materials for the smooth a-halogenation of ketones, which can be carried out by oxidation with A-halosuccinimides , halogens and iodoben-zenedifluoride or xenon difluorides. As shown in equation 32 , the reaction of 45 with Xep2 gives a 1 1 mixture of a-fluoroketone diastereoisomers 46a and 46b. 

Anodic oxidation couples the pendant arm and the silyl enolate fragments of 54 to give the annulated product 55 (equation 40) , a key intermediate in the synthesis of hamigerans, an unusual halogenated marine natural product . 

---